Make "Home" a formal application

Summary: Ref T3979. Currently, the home page lives in an old application called "directory" and is informally defined. Make it a real application called "Home", with a formal definition. It isn't launchable and can't be uninstalled.

Test Plan: Loaded home, saw exact same stuff.

Reviewers: chad, btrahan

Reviewed By: chad

CC: aran

Maniphest Tasks: T3979

Differential Revision: https://secure.phabricator.com/D8074