R1:86c399b65783

Rename `PhabricatorApplication` subclasses

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

Test Plan:
# Pinned and uninstalled some applications.
# Applied patch and performed migrations.
# Verified that the pinned applications were still pinned and that the uninstalled applications were still uninstalled.
# Performed a sanity check on the database contents.

Reviewers: btrahan, epriestley…