Use Source Sans for Phriction
Summary: Adds Phriction to list of apps that use Source Sans as default font in addition to Legalpad and Diviner.
Test Plan: Tested various layouts imported from secure. Should be reasonably tested, but will follow up on secure.
Reviewers: epriestley
Reviewed By: epriestley
Subscribers: epriestley, Korvin
Differential Revision: https://secure.phabricator.com/D10064