Restructure side nav

[veniosg]

• Side nav should now present two sections: Storage (which would include internal, external and in the future OTG storage) and Bookmarks.
• List should have headers (easy enough with RecyclerView)
• Settings and about should move up into the sidenav's Toolbar/Header as actions.
• Bookmarks' list should be able to update on a per item basis so there is an animation when adding a bookmark and automatically opening the drawer, making the action result clearer.
• As part of this, bookmarks should use an mvvm architecture, like the updated search.

Requires #73
Supersedes #54