Implemented option to allow users to view username of repository URIs.

Test Plan:
Enable the checkbox under the Tracking options for a repository.
View the repository in Diffusion, the username should show.

Reviewers: epriestley

Reviewed By: epriestley

CC: aran, Korvin

Maniphest Tasks: T2575

Differential Revision: https://secure.phabricator.com/D5269