Rationalise Geo naming of projects, repositories and paths

Geo classes and attributes are currently named a little confusingly. In particular:

• We use Repository in many places where we should use Project instead, and vice-versa
• We use path_with_namespace in many places where we should use disk_path instead

An example of the former is Geo::RepositorySyncWorker. It actually enqueues Geo::ProjectSyncWorker jobs, which run a ProjectSyncService per repository (oncee for the project repository, one for the wiki repository).

Then there's the Geo::RepositoryRenamedEvent (which should be a Geo::ProjectRenamedEvent), which has old_path_with_namespace and new_path_with_namespace - these should actually be old_disk_path and new_disk_path.

I'm sure there are other examples as well. We should gather a list and fix them all.

/cc @stanhu @brodock