Add a meta-application

Summary:

• Adds a new "Applications" application.
• Builds an application list via application config instead of via hard-coding, so we can move toward better concepts of installing/uninstalling applications, etc.
• Applications indicate that they need attention with notice counts and brief status messages rathern than 50 giant tables of all sorts of app data.

I want to try replacing the home screen with this screen, pretty much. Not sure if this is totally crazy or not. What does everyone else think?

Test Plan: Will add screenshots.

Reviewers: btrahan, chad, vrana, alanh

Reviewed By: vrana

CC: aran, davidreuss, champo

Maniphest Tasks: T1569

Differential Revision: https://secure.phabricator.com/D3129