Phriction setting.

Summary: One setting.

Test Plan:
- Looked at the setting in the web interface.
- Waved to it
- Introduced myself
- Had a nice conversation
- Made a new friend
- Turns out `phriction.enabled` is a nice guy.

Reviewers: epriestley, chad

Reviewed By: chad

CC: aran, Korvin

Maniphest Tasks: T2255

Differential Revision: https://secure.phabricator.com/D4436