Allow Differential Mail to accept multiple comments for one mail

Summary:
Ref T2222. Currently, one `DifferentialComment` can do a lot of things (add ccs, reviewers, comments, inline comments, and perform state changes). In the future, each `ApplicationTransaction` does only one thing. This is the primary piece of complexity which makes the upcoming migration risky, because each comment needs to migrate into multiple transactions.

I want to mitigate this complexity as much as possible before the migration itself happens. One approach I'm going to use to do that is to start writing one comment per effect now, so the mapping is more direct when the migration itself happens and the write code can be straightforward (one row per save()) after the migration.

This tackles a small piece of that, which is the mail Differential sends. Currently, Differential mail acts on a single comment. Instead, allow it to act on a list of comments, but always give it one comment for now. In the future, we can hand it several comments instead and still get the expected behavior.

This change should have no impact on any application behaviors.

Test Plan:
  - Commented;
  - commented with inline;
  - added reviewers;
  - added CCs;
  - added CCs via mentions;
  - updated revision;
  - looked at all the mail, all of which seemed sane.

Reviewers: btrahan

Reviewed By: btrahan

CC: aran

Maniphest Tasks: T2222

Differential Revision: https://secure.phabricator.com/D8199
Separate revision updates into two separate comments

Summary:
Ref T2222. Instead of writing one comment which performs both a diff update and adds a comment, write two comments, one for each action. These will translate directly into ApplicationTransactions writes.

This has a small impact on the UX: these updates now render in two rows, instead of one. After T2222, they'll automerge back together.

{F111909}

Test Plan: Updated a revision.

Reviewers: btrahan

Reviewed By: btrahan

CC: aran

Maniphest Tasks: T2222

Differential Revision: https://secure.phabricator.com/D8200
Write one DifferentialComment per CommentEditor action

Summary:
See D8200. Ref T2222. Instead of writing one comment which can have a ton of different effects, write a series of one-effect comments. These will be easier to convert into ApplicationTransactions.

This has a minor user-facing effect of making these multiple-action comments render separately:

{F111919}

Once the migration completes, they should automatically merge together nicely again.

Test Plan: Made a bunch of comments and took a bunch of actions, all of which worked normally except that they rendered as several things instead of just one.

Reviewers: btrahan

Reviewed By: btrahan

CC: aran, FacebookPOC

Maniphest Tasks: T2222

Differential Revision: https://secure.phabricator.com/D8201
Move Differential to proper subscriptions

Summary:
Ref T2222. Ref T4415. We're still writing Differential subscription stuff into this weird legacy `differential_relationship` table, which is like an edge table but extremely ancient.

Move it into a proper table.

I've removed `withSubscriptions()` from `DifferentialRevisionQuery`. It was weird, doesn't work consistently with other similar filters, and was only used by the API. Now it means "ccs", which is consistent with the ApplicationSearch UI and with Maniphest.

Test Plan:
Without migrating, added and removed subscribers via various workflows. Queried for subscribers. Everything worked as expected.

Ran the migration, verified data survived.

Reviewers: btrahan

Reviewed By: btrahan

CC: FacebookPOC, aran

Maniphest Tasks: T2222, T4415

Differential Revision: https://secure.phabricator.com/D8202
PHUITimelineView

Summary:
Updates PhabricatorTimeline to PHUITimeline. Uses standard colors and spacing, softens up the actors, and reduces visual spacing of action-only events.

- Also updated some 2x sprite images.

Test Plan: Tested Tasks Paste and Pholio in my sandbox.

Reviewers: epriestley, btrahan

Reviewed By: epriestley

CC: Korvin, epriestley, aran

Differential Revision: https://secure.phabricator.com/D8205
Fix issue where new transaction comments can be spread across multiple transactions

Summary: Ref T2222. We need this `clone` when constructing the new multi-comments in Differential, or we get double-comments internally. This shows up as emails with double comment text.

Test Plan: Sent some "Accept + comment" emails, only one comment in the body.

Reviewers: chad, btrahan

Reviewed By: chad

CC: aran

Maniphest Tasks: T2222

Differential Revision: https://secure.phabricator.com/D8206
Make chatlog bg white

Summary: More white, less whitesmoke.

Test Plan: rload chatlg

Reviewers: epriestley, btrahan

Reviewed By: epriestley

CC: Korvin, epriestley, aran

Differential Revision: https://secure.phabricator.com/D8207
Remove unreachable DifferentialRevisionStatsView

Summary:
Ref T2222. I wiped out the Differential-specific stats page a long time ago, but missed this. It turned up recently in `grep`.

Facts will eventually fill this role; this code is unreachable; it probably doesn't work now and definitely won't work in a day or two after ApplicationTransactions.

Test Plan: Used `grep` to look for callsites.

Reviewers: btrahan, chad

Reviewed By: btrahan

CC: aran

Maniphest Tasks: T2222

Differential Revision: https://secure.phabricator.com/D8208
Reduce reliance on `getRevisionID()` on DifferentialComment

Summary: Ref T2222. A few rendering interfaces rely on fishing the revision ID out of a DifferentialComment, but it will only have the PHID soon. Pass in the revision and use it to determine the ID instead.

Test Plan: Browsed, previewed, examined comments. Clicked anchors.

Reviewers: btrahan, chad

Reviewed By: btrahan

CC: aran

Maniphest Tasks: T2222

Differential Revision: https://secure.phabricator.com/D8209
Update Timeline for Tablet/Mobile

Summary: Minor CSS fixes Fixes T4419

Test Plan: Test phone and table breakpoints, submit a new comment.

Reviewers: epriestley, btrahan

Reviewed By: epriestley

CC: Korvin, epriestley, aran

Maniphest Tasks: T4419

Differential Revision: https://secure.phabricator.com/D8211
Fix timeline line

Summary: Accidentally removed the line

Test Plan: Test mobile AND desktop

Reviewers: epriestley

CC: Korvin, epriestley, aran

Differential Revision: https://secure.phabricator.com/D8212
Merge remote-tracking branch 'upstream/master' into release