Move main menu to dropdown
Motivation
On small mobile screens, the main menu takes a a large portion of the screen leaving only a small area for content. On an iPhone SE 3rd gen, for example, the usable section of the screen is less than half - screenshot.
Changes
This MR moves the main menu items into a dropdown menu which is collapsed by default.
Related Issues
Remaining Work
This MR does not fully address the issue described in lego#14 , it is still a little strange on those pages to have a main menu, breadcrumbs, and a sub-menu.