Repo registration (with Scalar.Service) should happen during scalar clone rather than mount.

Additionally, the clone verb itself should update the registration file (or each clone should create its own file) and Scalar.Service should read the file(s) to discover which repos have been registered.

Additionally:

• Scalar.Service should also remove repos when it finds they're no longer on disk.
• There should be a verb for manually registering/unregistering repos
• Functional tests should not register when cloning or they should register in a test location that does not impact the installed Scalar.Service