Refactor diffs

This refactoring done on top of Marin improvements to side-by-side diff.
Main target of this refactoring is to reduce mess and increase test coverage.

1. Use objects:
  * Gitlab::Diff::Line for line change in diff
  * Gitlab::Diff::File for file changes (diff + blob info)
2. Avoid `yield` magic
3. Move logic from views/helper to models/libs
4. Move diff views under separate dir `app/views/projects/diffs`

See merge request !1072

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

add current sign-in date

Prevent graph spacing issue

Switch from travis to semaphoreapp

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

Added cmake and pkg-config as build dependency for pkgr

Add comment to merge request when new push happens

Fixes #1494

See merge request !1065

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

It allows track when user added new commits to existing merge request
Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

added htmlsafe to branch list

change git to git bin path

Delete mailer queue

Show labels help message if last label is deleted

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>