Toggle app navigation not only on mobile, but on desktop as well

Several reasons for this:
* We now have a sidebar in Files, so there’s two sidebars taking space (most other apps have a sidebar already).
* The app navigation is arguably not needed all the time.
* If you have many apps installed, scrolling on the app navigation is clunky and gets ugly fast (too thin)
* If you don’t have many apps installed, it looks like a waste of space (like for the Enterprise Edition)
* We give apps the whole width, which alleviates a lot of issues we had in the past with CSS and sizing