Replace Differential hard-coded status "<select />" with tokenizer

Summary:
Ref T2543. This updates the UI control in the web UI. Also:

• This implicitly makes this queryable with the API (differential.revision.search); it previously was not.
• This does NOT migrate existing saved queries. I'll do those in the next change, and hold this until it happens.
• This will break some existing /differential/?status=XYZ links. For example, status=open now needs to be status=open(). I couldn't find any of these in the upstream, and I suspect these are rare in the wild (users would normally link directly to saved queries, not use URI query construction).

Test Plan:

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T2543

Differential Revision: https://secure.phabricator.com/D18393