Sort repositories in Diffusion by name, not creation order

Summary: Ref T2298. This seems like the least complicated reasonable order to implement.

Test Plan: Looked at repositories, saw them ordered by name.

Reviewers: vrana, btrahan, brennantaylor

Reviewed By: btrahan

CC: aran

Maniphest Tasks: T2298

Differential Revision: https://secure.phabricator.com/D4395