Use a function typeahead for "projects" in Maniphest

Summary: Ref T4100. Collapse the five inputs into one.

Test Plan:

• Searched for a bunch of stuff.
• Used "Group By: Project", which is a bit of a special case and possibly tricky.
• Created an old query with all the fields, then updated; verified it was preserved/transformed correctly.

Reviewers: btrahan

Reviewed By: btrahan

Subscribers: epriestley

Maniphest Tasks: T4100

Differential Revision: https://secure.phabricator.com/D12525