Use GET form in Owners search

Summary:
The form doesn't perform any action, only displays data.
URL wouldn't exceed its maximum length.
Bookmarking results can be useful.
Linking from other pages can be even more useful.
Also browsing through history is more fluent.

Test Plan:
Search by path.
Search by owner.

Reviewers: epriestley

Reviewed By: epriestley

CC: aran, epriestley

Differential Revision: https://secure.phabricator.com/D1559