Despecialize most task status handling

Summary: Ref T1812. Moves most specialized status handling into ManiphestTaskStatus. The only real missing case is reports.

Test Plan:
Browsed most of the affected interfaces. Changed task status:

Reviewers: btrahan

Reviewed By: btrahan

Subscribers: epriestley

Maniphest Tasks: T1812

Differential Revision: https://secure.phabricator.com/D8579