Move Repositories to SearchField

Summary: Ref T8441. Ref T7715. Internalizes setQueryOrder(). Removes appendOrderFieldsToForm().

Test Plan: Used all Repository search fields.

Reviewers: btrahan

Reviewed By: btrahan

Subscribers: epriestley

Maniphest Tasks: T7715, T8441

Differential Revision: https://secure.phabricator.com/D13196