Provide revision parent/child edges in edge.search, and more information in differential.revision.search

Summary: See PHI195. This bulks out these API methods since all the requests are pretty straightforward.

Test Plan: Ran edge.search and differential.revision.search.

Reviewers: amckinley

Reviewed By: amckinley

Differential Revision: https://secure.phabricator.com/D18762