Makes the following changes in order to have all the
items of the top nav fit within all of the new Bootstrap 4 breakpoints:

- Change GitLab logo to show only on desktop breakpoint (lg and up)
  - Move margin from logo to logo text, saving 8px
- Move the following icon links to the "More" nav dropdown
  - Instance Statistics (ConDev Index)
  - Admin area (if Admin)
  - Sherlock Transactions (if enabled)
- Removed separator between Admin icons
- Change search input width from 240px to 200px
- Move "Activity", "Milestone", and "Snippets" into "More" menu on lg breakpoints
- Show "More" menu of lg breakpoints