Modernize "owner" typeahead datasource

Summary: Ref T4420. This one is users plus "upforgrabs". I renamed that to "none" and gave it a special visual style to make it more discoverable. Future diffs will improve this.

Test Plan:
  - Used it in global search.
  - Used it in batch editor.

Reviewers: btrahan

Reviewed By: btrahan

Subscribers: epriestley

Maniphest Tasks: T4420

Differential Revision: https://secure.phabricator.com/D9891