Provide more API information about Maniphest task statuses and priorities

Summary: Ref T9964. Priorities and statuses have metadata (colors, names, etc) which we can reasonably just return from API callers. This is so ligthweight that I think it doesn't really make sense to put in an attachment. We also use this information in arc tasks.

Test Plan: Called API, got sensible looking status and priority data back.

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T9964

Differential Revision: https://secure.phabricator.com/D14777