Add support for branch-related configuration to new Repository edit workflow
Summary: Ref T2231. Modernizes editing "Default Branch", "Track Only", and "Autoclose Only".
Test Plan: See screenshots.
Reviewers: btrahan, chad
Reviewed By: btrahan
CC: aran
Maniphest Tasks: T2231
Differential Revision: https://secure.phabricator.com/D7399