Improve Monokai highlight style to match original

The current monokai style in highlightjs is not very true to the
original and lacks colors for certain syntactic items. This change's
goal is to bring the highlightjs monokai style in line with the original
design from http://www.monokai.nl/blog/2006/07/15/textmate-color-theme/
Prevent 500 on MR page if merge_event missing

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>
Decline push if repository does not exist

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>
Bolder event title and lighter color for event body

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>
Execute project services asynchronously

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>
Merge branch 'async-services' into 'master'

Async services

Fixes #1814

See merge request !1312
Merge branch 'small-fixes' into 'master'

Small fixes

Improve application stability over unexpected cases

See merge request !1310
Merge branch 'improve-activity-ui' into 'master'

Improve activity UI

See merge request !1311
Merge branch 'improved-monokai' into 'master'

Improve Monokai highlight style to match original

The current monokai style is not very true to the original and lacks colors for certain syntactic items as mentioned in ticket https://github.com/gitlabhq/gitlabhq/issues/6855. This change's goal is to bring the monokai highlight style in line with the original design from http://www.monokai.nl/blog/2006/07/15/textmate-color-theme/

Before:
![monokai-old](https://gitlab.com/uploads/klowner/gitlab-ce/ce96c7d7c2/monokai-old.png)

After:
![monokai](https://gitlab.com/uploads/klowner/gitlab-ce/b257a8143a/monokai.png)

See merge request !238