Showing tasks & diffs in the typeahead.

Summary: Trying to show tasks & diffs in the typeahead. My brain has got dumber as I have not been in touch with phab dev. Waiting for your comments and pointers.

Test Plan:
{F47352}
The tasks should show up in the type-ahead.

Reviewers: epriestley, Afaque_Hussain

Reviewed By: epriestley

CC: aran, Korvin, AnhNhan, blc

Maniphest Tasks: T2948

Differential Revision: https://secure.phabricator.com/D6175