[Workbench] Project listings act like file manager directory trees, with expanding+collapsing trees
Whenever a project listing appears (e.g., in the topnav pulldown, or in object choosers), it should be presented as a tree. It should act like a directory tree in a file manager, where you can collapse and expand projects to navigate the tree.
- The menu is rendered as you go as you expand projects. This way, Workbench only needs to do a small number of API queries to render the initial tree. When you expand a project, Workbench makes an AJAX call to list that project's subprojects, and renders the result once it's returned.
- If you're viewing a project, or an object inside a project, when you open the project listing, it should start centered on that project, with parent projects expanded as necessary all the way up to home.
- In any other case, the listing should start by rendering the Home project and its immediate subprojects, all collapsed. The view should be at the top of the listing, so the Home project is visible.