Improve and finish the fallback to the In-Reply-To and References header for the reply-by-email feature

A few things to note:
- The IncomingEmail feature is now enabled even without a
  correctly-formatted sub-address
- Message-ID for new thread mail are kept the same so that subsequent
  notifications to this thread are grouped in the thread by the email
  service that receives the notification
  (i.e. In-Reply-To of the answer == Message-ID of the first thread message)
- To maximize our chance to be able to retrieve the reply key, we look
  for it in the In-Reply-To header and the References header
- The pattern for the fallback reply message id is "reply-[key]@[gitlab_host]"
- Improve docs thanks to Axil

Clarify LFS configuration

A user on Twitter was confused (rightfully so) because LFS admin docs suggest you must set a storage path. In fact, Omnibus defaults to a very sane location. Add a comment to the snippet outlining the default.

See merge request !3388

Fix cancel button on issuable edit form

See merge request !3392

Comments on confidential issues doesn't show in activity feed to non-members

Closes #14568 

See merge request !3375

Fixed issue with width of project select dropdown

Before:

![Screen_Shot_2016-03-24_at_13.42.53](/uploads/25580c45dc339f7f932f032ac2d10fba/Screen_Shot_2016-03-24_at_13.42.53.png)

![Screen_Shot_2016-03-24_at_13.43.04](/uploads/e4d1d4e332d27f14c980264bef9dc4d9/Screen_Shot_2016-03-24_at_13.43.04.png)

After:

![Screen_Shot_2016-03-24_at_13.42.38](/uploads/68b8e161d86b41849f9e8a1d9c8fd36c/Screen_Shot_2016-03-24_at_13.42.38.png)

![Screen_Shot_2016-03-24_at_13.43.13](/uploads/f3fe732bcd517efea3a1d7c761bb6a0e/Screen_Shot_2016-03-24_at_13.43.13.png)

See merge request !3386

Fixed bold in sidebar

![Screen_Shot_2016-03-23_at_12.01.54](/uploads/d50ae3426efcb2436b3debdd80073b2f/Screen_Shot_2016-03-23_at_12.01.54.png)

This is to go with https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/289

See merge request !3358

Shows password form when signed in with linked account

Closes #14379

Doing this to get the builds passing for !3325

See merge request !3381

Explain why ExclusiveLease has no #cancel

[ci skip]

See merge request !3383

Merge branch 'add-tooltip-to-issue-new-branch-button-with-create-branch-issue-title-123-14565' into 'master'

Add tooltip to new branch button

Closes #14565

See merge request !3380

[ci skip]

Closes #14379

Fix specs broken by !3270 and !3337.

To be fair:

- !3270 modifies CSS but `scss-lint` job was allowed to fail in the MR, while not allowed in `master`
- !3337 modifies HTML but the broken test was only in `master` at the time

/cc @alfredo1 @iamphill 

See merge request !3378

Dropdown pixel perfect 🎉

Closes #14333, #14331, #14472, #14515 

See merge request !3337

Documentation: SCSS Style Guide fixes

Fixed a typo and added a section on ignoring issues.

[ci skip]

See merge request !3263

Fix a typo and add a section on ignoring issues.

[ci skip]

Crop avatars on the client before upload

<img src="/uploads/535d69956cc5904870ae5d95132a35af/Screen_Shot_2016-03-17_at_9.55.56_AM.png" width="700">

closes #7959
closes #600 

See merge request !3270

Issue sidebar overlaps on tablet

Closes #14180

![Screen_Shot_2016-03-18_at_13.10.53](/uploads/d1e81778740a034aa98c881a70e55254/Screen_Shot_2016-03-18_at_13.10.53.png)

See merge request !3299

Multi-update issues tests

There were no tests for updating multiple issues at a time - this fixes
that 👍 

See merge request !3357

Fix missing tooltip in project title

closes #14516 

![tooltip](/uploads/121cc3676f4f32044e158cf5f3df5be5/tooltip.gif)

See merge request !3351

Add special cases for built-in Rails routes in development



See merge request !3369

Fixed error with applications delete anonymous token form

Closes #14509 

See merge request !3362

Moved the scss out of a mixin as it was really confusing the hell out of the CSS

Strip commit title when creating revert commit.

Fixes #14453 

See merge request !3352

Fix Milestone.upcoming

The order wasn't happening because of `default_scope`. Blegh.

See merge request !3364