Add relation between project and remote repoistory objects

[agjohnson]

This will be used with the webhook additions to more tightly couple projects and
data from GitHub. For webhooks, this work will allow us to explicitly tell how
the project is connected to the GitHub/Bitbucket/etc repo, and will allow for
explicit resyncing of the webhook as well.

This overhauls the testing of the project import wizard, both the wizard and the tests were doing a lot of things that weren't required or were straight up incorrect. The tests are now based on client factories, because it was too difficult to debug failing tests otherwise. This exposed a number of places that the wizard view was doing some wrong things however, so seems more complete.

Refs #1895

[agjohnson]

Noticed the relation in this model is off, we don't want cascade delete on remote repo objects here as it leads to a missing repo on project removal.

[ericholscher]

Looks great -- should we also be doing something to reset the remote repos on webhook? Seems like we probably want to backport this data onto the existing projects, not just set it for new ones.

[agjohnson]

There isn't a great way to do that and ensure the repo is correct. I was considering a later follow up to this would be to replace the repo URL in the project admin with another remoterepo form, so the project could later be reconnected to another repository. I'm not sure if that is the correct UX though.

For the purpose of webhooks, not have every project connected to a remoterepo works just fine. We need to be able to detect if a project has any connection to a remote repo to determine if we can set up a webhook at all, or if the user should handle it manually.

If we find it useful, this is something that could be done separately