Perform commit message parsing and construction with new CustomFields

Summary: Ref T2222. Ref T3886. Converts parsing and construction of commit messages to be driven by CustomField.

Test Plan:
This is a huge, messy change. I've made an effort to test it exhasutively, but suspect I probably missed a few behaviors. Roughly:

  - Enumerted all current fields (fields implementing `shouldAppearOnCommitMessage()`) and tried to test them one by one.
  - Used `arc diff --edit` repeatedly to manipulate each field (this workflow hits both the parse and construct steps).
  - Used `arc amend --show` to examine construct output (this does not activate the "edit" mode).

Reviewers: btrahan

Reviewed By: btrahan

CC: aran

Maniphest Tasks: T3886, T2222

Differential Revision: https://secure.phabricator.com/D8449
Allow configuration of Differential custom fields

Summary: Ref T2222. Ref T3886. This is a little early for general use, but the message parse/generate stuff requires CustomFields and FieldSpecifications to be closely aligned, so this provides at least a plausbile approach for any installs that run into trouble.

Test Plan: Viewed config; reordered fields.

Reviewers: btrahan

Reviewed By: btrahan

CC: aran

Maniphest Tasks: T2222, T3886

Differential Revision: https://secure.phabricator.com/D8450
Use CustomField for `differential.updaterevision`

Summary: Ref T2222. Ref T3794. Medium term goal is to remove `DifferentialRevisionEditor`. This removes one of two callsites.

Test Plan: Used `arc diff --edit` to repeatedly update a revision, making changes to various fields.

Reviewers: btrahan

Reviewed By: btrahan

CC: aran

Maniphest Tasks: T3794, T2222

Differential Revision: https://secure.phabricator.com/D8451
Use CustomFields in `differential.createrevision`

Summary:
Ref T2222. Ref T3886. Medium term goal is to remove `DifferentialRevisionEditor`.

This temporarily reduces a couple of pieces of functionality unique to the RevisionEditor, but I'm going to go clean those up in the next couple diffs.

Test Plan: Used `arc diff --create` to create several revisions with different data.

Reviewers: btrahan

Reviewed By: btrahan

CC: aran

Maniphest Tasks: T3886, T2222

Differential Revision: https://secure.phabricator.com/D8452
Use DifferentialRevisionEditor in lipsum

Summary: Ref T2222.

Test Plan: Generated revisions with `bin/lipsum`.

Reviewers: btrahan

Reviewed By: btrahan

CC: aran

Maniphest Tasks: T2222

Differential Revision: https://secure.phabricator.com/D8453
Remove willWriteRevision/didWriteRevision hooks

Summary:
Ref T2222. DifferentialRevisionEditor has no remaining callsites, but it has a bit of functionality which still needs to be ported forward. I'm going to rip it apart piece by piece.

This removes the willWriteRevision/didWriteRevision hooks. They are completely encapsulated by transactions now, except for a unique piece of branch/task logic, which I migrated forward.

Test Plan:
  - Lots of `grep`.
  - Created a new revision on branch `T25`, saw it associate with the task.

Reviewers: btrahan

Reviewed By: btrahan

CC: aran

Maniphest Tasks: T2222

Differential Revision: https://secure.phabricator.com/D8454
Perform derived index updates in TransactionEditor

Summary: Ref T2222. We have two tables (one for hashes; one for paths) which were unevenly updated before. Now, update them consistently in the TransactionEditor.

Test Plan: Created a revision, saw it populate this information.

Reviewers: btrahan

Reviewed By: btrahan

CC: aran

Maniphest Tasks: T2222

Differential Revision: https://secure.phabricator.com/D8455
Remove DifferentialRevisionEditor

Summary: Ref T2222. This has no callsites and no functionality not present in the TransactionEditor.

Test Plan: awwyiss

Reviewers: btrahan

Reviewed By: btrahan

CC: aran

Maniphest Tasks: T2222

Differential Revision: https://secure.phabricator.com/D8456
Modernize commit message tips

Summary: Ref T2222. Fully modernizes these tips. No callsites remain for the old methods.

Test Plan: `grep`

Reviewers: btrahan

Reviewed By: btrahan

CC: aran

Maniphest Tasks: T2222

Differential Revision: https://secure.phabricator.com/D8457
Port Differential mail features forward to transactions

Summary:
Ref T2222. Brings the major mail features (affected files, patches) forward.

This drops some of the minor integrations which just show object state (like "Maniphest Tasks") since I think they're not very important. I'll put them back if users miss them.

Test Plan: Sent mail with inline/attached patches.

Reviewers: btrahan

Reviewed By: btrahan

CC: aran

Maniphest Tasks: T2222

Differential Revision: https://secure.phabricator.com/D8459
Remove host/path and test plan enable/disable options

Summary: Ref T2222. These no longer have an effect, and are obsoleted by `differential.fields`.

Test Plan: `grep`

Reviewers: btrahan

Reviewed By: btrahan

CC: aran

Maniphest Tasks: T2222

Differential Revision: https://secure.phabricator.com/D8468
Use CustomFields to power Conduit auxiliary dictionaries

Summary: Ref T2222. Moves this Conduit stuff over.

Test Plan: Made Conduit calls, saw data in results.

Reviewers: btrahan

Reviewed By: btrahan

CC: aran

Maniphest Tasks: T2222

Differential Revision: https://secure.phabricator.com/D8469
Remove field selector on Diff view and Revision List View

Summary:
Ref T2222. This has some minor functionality regressions:

  - The plain diff page no longer shows unit/test status. I want to give diffs separate custom fields for this.
  - It was technically possible to shove more data on the list view, although this doensn't affect the default config.

Test Plan: Looked at list view, diff detail view. Grepped for changes.

Reviewers: btrahan

Reviewed By: btrahan

CC: aran

Maniphest Tasks: T2222

Differential Revision: https://secure.phabricator.com/D8470
Move "close tasks on commit" code out of field specification stuff

Summary: Ref T2222. There's some magic here, just port it forward in a mostly-reasonable way. This could use some refinement eventually.

Test Plan: Pushed commits with "Fixes" and "Ref" language, used `reparse.php` to trigger the new code. Saw expected updates in Maniphest.

Reviewers: btrahan

Reviewed By: btrahan

CC: aran

Maniphest Tasks: T2222

Differential Revision: https://secure.phabricator.com/D8471
Remove DifferentialFieldSelector

Summary: Ref T2222. Gets rid of DifferentialFieldSelector, favoring `differential.fields`.

Test Plan: `grep`

Reviewers: btrahan

Reviewed By: btrahan

CC: aran

Maniphest Tasks: T2222

Differential Revision: https://secure.phabricator.com/D8472
Use PhabricatorObjectListQuery in Herald worker

Summary: Ref T2222. Straightforward, just breaks a needless dependency.

Test Plan: Pushed and parsed a commit with "Auditors" in it.

Reviewers: btrahan

Reviewed By: btrahan

CC: aran

Maniphest Tasks: T2222

Differential Revision: https://secure.phabricator.com/D8473
Remove almost all old Differential field code

Summary: Ref T2222. The unit and lint fields still have one piece of functionality that I need to port, but everythign else is obsolete.

Test Plan: Lots of `grep`.

Reviewers: btrahan

Reviewed By: btrahan

CC: aran

Maniphest Tasks: T2222

Differential Revision: https://secure.phabricator.com/D8474
Move lint/unit test warning code forward to Transactions

Summary: Ref T2222. Makes the "lint/unit errors" warnings work again.

Test Plan: Viewed some revisions with and without these warnings.

Reviewers: btrahan

Reviewed By: btrahan

CC: aran

Maniphest Tasks: T2222

Differential Revision: https://secure.phabricator.com/D8475
Clean up various pieces of dead/obsolete Differential code

Summary:
Ref T2222.

  - Removes `DifferentialTasksAttacher`, which has had no callsites for a very long time.
  - Moves `differential.getrevisioncomments` off `DifferentialCommentQuery`.
  - Moves Releeph churn field off `DifferentialCommentQuery`.
  - Removes dead code in `DifferentialRevisionViewController`.
  - Removes `DifferentialException` (no references).
  - Removes `DifferentialRevision->loadComments()` (no callsites).
  - Removes `DifferentialRevision->loadReviewedBy()` (all callsites updated).
  - Removes `DifferentialCommentQuery` (all callsites updated).

Test Plan: Mostly a lot of `grep`.

Reviewers: btrahan

Reviewed By: btrahan

CC: aran

Maniphest Tasks: T2222

Differential Revision: https://secure.phabricator.com/D8476
Remove DifferentialComment

Summary: Ref T2222. Remove this; no more callsites.

Test Plan: `grep`

Reviewers: btrahan

Reviewed By: btrahan

CC: aran

Maniphest Tasks: T2222

Differential Revision: https://secure.phabricator.com/D8477