Update links in side nav and header

* Remove todos, help, and project settings from sidebar
* Remove plus icon from top right header
* Put help link in user dropdown
* Add lighter bg-color at the top of side nav

![Screen_Shot_2016-10-27_at_3.42.55_PM](/uploads/d81f3135b1af1e580d62451ae83b3435/Screen_Shot_2016-10-27_at_3.42.55_PM.png) 
Closes #22889

See merge request !7161