R1:08687c0b172d

Search options.

Test Plan:
- Looked at the new options
- Saved `search.engine-selector` successfully.

Reviewers: epriestley, chad, btrahan

Reviewed By: epriestley

CC: aran, Korvin

Maniphest Tasks: T2255

Differential Revision: https://secure.phabricator.com/D4410