Remove application small/hidden tiles

Summary:
Ref T5176. This paves the way for the redesign by making the homepage editor thing a little more manageable/coherent.

Not perfect, but we can clean it up a bit after the new design.

Test Plan:
Home page:

New "Pinned Applications" settings panel (this supports drag-and-drop to reorder):

Pin an app:

Unpin an app:

Reviewers: btrahan, chad

Reviewed By: chad

Subscribers: epriestley

Maniphest Tasks: T5176

Differential Revision: https://secure.phabricator.com/D9332