Releeph s/isPusher/isAuthoritative/

Summary: Instead of being able to ask if someone was a pusher or not, ask if they are "authoritative" enough to make decisions about Releeph requests. A person is authoritative if a project has pushers, and they are a pusher, or in the case of pusher-less projects, everyone is authoritative.

Test Plan: Make a request in a project with no pushers (it is immediately ready to be picked) and a project with pushers (where it requires approval.)

Reviewers: wez, epriestley

Reviewed By: epriestley

CC: epriestley, aran

Differential Revision: https://secure.phabricator.com/D5877