Cheat my way through the rest of the typeahead datasources

Summary:
Ref T5750. These are a pain to modernize and most don't matter, so cheat:

• Mark a bunch nonbrowsable, including some that probably should be browsable but which I don't want to deal with for now.
• For static datasources, add an easy server-side filter (this isn't really cheating, and is appropriate for the status/priority/application datasources).
• Make composite sources browsable if their components are browsable.

Test Plan:

• Tried to browse an unbrowsable source, got a 404.
• Browsed a composite source.
• Browsed static sources (priority/status/applications).
• Browsed normal sources (people/projects).

Reviewers: btrahan

Reviewed By: btrahan

Subscribers: epriestley

Maniphest Tasks: T5750

Differential Revision: https://secure.phabricator.com/D12438