responsive sidebar
responsive sidebar on dashboard
add responsive sidebar to issues, milestones and MRs
Remove garbage and apply wiki style

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

Cleanup help

Remove a lot of unused help files.
Apply `wiki` css to help content
Merge branch 'responsive-sidebar' into 'master'

Responsive sidebar

Puts the sidebar on the dashboard in a off-screen sidebar that can be called by pressing a button with a fixed position.

Any sidebar with the .responsive-sidebar class will follow this behavior. Button must be added manually.