Remove gray background from layout
Fix for #6061 (closed)
Why?
- make it looks nice
- focus on content, not design
- simplify css
- make less difference between fixed and fluid layout by using fluid components like gray bg for project/user pages
- preparation for new issue/merge request page with sidebar (see https://gitlab.com/gitlab-org/gitlab-ce/issues/3981#note_3132797)
Extra changes
As part of changing layout I was forced to touch navigation class. Because it was a mess I refactored it in one css class nav-list. 4 similar css classes were removed like center-top-menu, center-middle-menu etc. Also I removed usage of nav-tabs and nav-pills. /help/ui page was updated to follow changes.