Rename PhabricatorApplication subclasses

Summary: Ref T5655. Some discussion in D9839. Generally speaking, Phabricator{$name}Application is clearer than PhabricatorApplication{$name}.

Test Plan:

1. Pinned and uninstalled some applications.
2. Applied patch and performed migrations.
3. Verified that the pinned applications were still pinned and that the uninstalled applications were still uninstalled.
4. Performed a sanity check on the database contents.

Reviewers: btrahan, epriestley, #blessed_reviewers

Reviewed By: epriestley, #blessed_reviewers

Subscribers: hach-que, epriestley, Korvin

Maniphest Tasks: T5655

Differential Revision: https://secure.phabricator.com/D9982