Return project phids when making repository.query calls. This allows
conduit clients to access the repo<-->project mapping. Also allow
querying by project phids for symmetry.

Calling needProjectPHIDs on every needProjectPHIDs may make them more
expensive but this method is already marked as unstable and adding
some new repoistory.query.withprojects method sounds ugly and
complicated.

• Use a phabricator instance where some repos have projects
• Query for a repo by callsign, observe projects array has something that looks like a phid
• Query project.query with the phid to make sure it's something valid
• Query for a repo by project, should return only repos with that project
• Query for a repo with no projects, observe a nice empty projects array.