Do not publish/notify about commits which are not reachable from any "Autoclose" ref

Summary:
Depends on D20418. Ref T13277. Fixes T11314.

Currently, when you push commits to some arbitrary ref or tag (like refs/pull/123 on GitHub, refs/tags/phabricator/diff/123 on Phabricator, or refs/changes/whatever on Gerrit), we do not "autoclose" related objects. This means that we don't process Ref T123 to create links to tasks, and don't process Differential Revision: xyz to close revisions.

However, we do still publish these commits. "Publish" means: trigger audits, publish feed stories, and run Herald rules.

• Stop publishing these commits.
• In the UI, show these commits as "Not Permanent" with a note that they are "Not [on any permanent branch]."

These commits will publish and autoclose if they ever become reachable from an "autoclose" ref (most commonly, if they are later merged to "master").

Test Plan:

• Pushed a commit to refs/tags/quack.
• Before: got a feed story.
• After: no feed story, UI shows commit as "Not Permanent".

Reviewers: amckinley

Reviewed By: amckinley

Maniphest Tasks: T13277, T11314

Differential Revision: https://secure.phabricator.com/D20419