Align most revision actions to the new "Draft" state

Summary:
Ref T2543. Most actions are not available for drafts.

Authors can "Request Review" (move out of draft to become a normal revision) or "Abandon".

Non-authors can't do anything (maybe we'll let them do something later -- like "Commandeer"? -- if there's a good reason).

Test Plan: Viewed a draft revision as an author and non-author, saw fewer actions available.

Reviewers: amckinley

Reviewed By: amckinley

Maniphest Tasks: T2543

Differential Revision: https://secure.phabricator.com/D18626