Give "Autoclose Only" repository detail proper getters/setters

Summary:
Ref T13222. See D19829. We're inconsistent about using getDetail()/setDetail() to do some ad-hoc reads. Put this stuff in proper accessor methods.

Also a couple of text fixes from D19850.

Test Plan: Set, edited, and removed autoclose branches from a repository. Got sensible persistence and rendering behavior.

Reviewers: amckinley

Reviewed By: amckinley

Maniphest Tasks: T13222

Differential Revision: https://secure.phabricator.com/D19856