R1:7de17fb75ec3

Modernize tag and branch controllers in Diffusion

Summary: Ref T4245. Prepares these controllers to accept alternate identifers, plus minor spacing and layout fixes.

Test Plan: Viewed tags, viewed branches.

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T4245

Differential Revision: https://secure.phabricator.com/D14941