Assign PHIDs to all diffs

Summary:
Ref T1049. Ref T2222. `DifferentialDiff` does not currently have a PHID, but we need it for Harbormaster and ApplicationTransactions. See some discussion in D7501.

(I split the SQL into two sections so we can't fail in the middle. At some point, I'd like to do a pass on the migration stuff and get this happening automatically, and also simplify the PatchList.)

Test Plan:
  - Ran `bin/storage upgrade`.
  - Checked for valid PHIDs in the database.
  - Used `phid.query` to look up a diff by PHID.
  - Created a new diff and verified it got a PHID.

Reviewers: btrahan, hach-que

Reviewed By: btrahan

CC: aran, vrana

Maniphest Tasks: T2222, T1049

Differential Revision: https://secure.phabricator.com/D7513
Update WePay API to HEAD

Summary: This is mostly to pick up the LICENSE file for packaging purposes,
but also fixes a bug I reported.

Auditors: btrahan
Nuance - get some scaffolding up there

Summary:
I updated the wiki too - https://secure.phabricator.com/w/projects/pebkac/ - with what I am thinking right now. Rough plan here is

 - next diff:
  - implement editors and transactions
  - implement "web type" for contact source
   - /pebkac/item/new/ will be the entry point for this
  - implement "actions" on a contact
  - probably some "polish" on the scaffolding laid out here; like "create" permissions maybs
 - diffs after that:
  - implement "twitter" type for source
  - implement email reply handler stuff for item and source

Probs a great time to blast huge holes in all this stuff. :D

Test Plan: these pages load and arc lint doesn't complain

Reviewers: epriestley

Reviewed By: epriestley

CC: Korvin, epriestley, aran, chad

Differential Revision: https://secure.phabricator.com/D7465
Move Mercurial discovery to PhabricatorRepositoryDiscoveryEngine

Summary: Ref T4068. Partly, this moves discovery to the more unit-testable PhabricatorRepositoryDiscoveryEngine. It also fixes some issues, see inlines.

Test Plan: In a Mercurial repository, ran `bin/repository discover --repair`, verified commits came out topographically sorted. Ran without `--repair` and in various other contexts, like with no commits to discover and some-but-not-all commits to discover.

Reviewers: btrahan

Reviewed By: btrahan

CC: aran

Maniphest Tasks: T4068

Differential Revision: https://secure.phabricator.com/D7518
Split Diffusion VSC serve code into its own controller

Summary: This is starting to get a bit sizable and it turns out Mercurial is sort of a beast, so split the VCS serve stuff into a separate controller.

Test Plan: Pushed and pulled an authenticated Git repository.

Reviewers: btrahan

Reviewed By: btrahan

CC: aran, hach-que

Differential Revision: https://secure.phabricator.com/D7494
Allow Phabricator to serve Mercurial repositories over HTTP

Summary: Ref T2230. This is easily the worst thing I've had to write in a while. I'll leave some notes inline.

Test Plan: Ran `hg clone http://...` on a hosted repo. Ran `hg push` on the same. Changed sync'd both ways.

Reviewers: asherkin, btrahan

Reviewed By: btrahan

CC: aran

Maniphest Tasks: T2230

Differential Revision: https://secure.phabricator.com/D7520