(Redesign) Clean up older "Tile" code

Summary:
This does some backend cleanup of the tile stuff, and some general cleanup of other application things:

• Users who haven't customized preferences get a small, specific set of pinned applications: Differential, Maniphest, Diffusion, Audit, Phriction, Projects (and, for administrators, Auth, Config and People).
• Old tile size methods are replaced with isPinnnedByDefault().
• Shortened some short descriptions.
• shouldAppearInLaunchView() replaced by less ambiguous isLaunchable().
• Added a marker for third-party / extension applications.

Test Plan: Faked away my preferences and viewed the home page, saw a smaller set of default pins.

Reviewers: chad

Reviewed By: chad

Subscribers: epriestley

Differential Revision: https://secure.phabricator.com/D9358