R1:e34a44a7ed15

Allow repository lookup by remote URI

Summary: This helps us move away from arcanist projects in normal use, by allowing us to identify repositories based on the remote URI.

Test Plan: Used `repository.query` to query some repos by remote URI.

Reviewers: btrahan

Reviewed By: btrahan

CC: aran

Differential Revision: https://secure.phabricator.com/D8069