Cleanup Typeahead and Global Search Typeahead

Summary:
- Makes text larger (12px, 13px)
- Makes global search match notifications container look
- Makes the jx typeahead feel a bit more attached, and similar to tokens and other inputs.

Test Plan: Tested global search and jx typeahead in maniphest.

Reviewers: epriestley, btrahan

Reviewed By: epriestley

CC: aran, Korvin

Differential Revision: https://secure.phabricator.com/D5939