Add "repository.create" and "repository.query" methods to Conduit

Summary: Primarily for @csilvers who has 92 million repositories or something. This is a touch hacky, but movitated by pragmatism.

Test Plan:

• Ran "repository.create" to create repositories, "repository.query" to list them.
• Tested most or maybe all of the error conditions, probably.

Reviewers: btrahan, vrana, csilvers

Reviewed By: csilvers

CC: aran

Differential Revision: https://secure.phabricator.com/D2396