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

* Squash project users selectbox and users selectbox into one class
* Move from API autocomplete to GitLab internal one
* Smarter filter for project/group/all issues
* Use selectbox with searchbox for assignee/author/milestone/label
* Switch to ajax filter for issue author/assignee

It is same search like we have at issues page. It allows to quickly
filter merge requests based on title or desription. I copy-pasted some
js code from Issues.js. In future search (filtering) logic should be
refactoed into one class for merge requests and issues

Use the path helpers for nested project resources, for Rails 4.1.9
compatibility.

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

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

move all sidebars to one side for improved UX; add button in head of projects/issues and milestones instead of tab on side of screen to prevent overlapping of content

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

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

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

- remove admin kaminari theme. Use gitlab theme everywhere
- use bootstrap styled for gitlab admin themes
- dont reload page when change issue filter