When "Fetch Refs" are configured for a repository, highlight the "Branches" menu item in the Diffusion Management UI

Summary: Ref T13448. Minor UI issue: setting a "Fetch Refs" value does not highlight the associated menu item, but should.

Test Plan: Set only "Fetch Refs", now saw menu item highlighted.

Maniphest Tasks: T13448

Differential Revision: https://secure.phabricator.com/D20895