Adds a Url property to the RemoteUpdater, which allows the remote url to...

... be updated.

This is a PR for issue #788 

Includes a single test case for verifying that the remote url was indeed changed.
Let me know if anything needs to be changed or corrected for this PR.
Actually, scrap that, don't even save the url locally. You have the remote saved so you can just do remote.Url everywhere.