Refactor references to how we name repositories #87

Moved from gitberg-temp/issues/15

Observation: the places we store repo_name are proliferating. In yaml, it's _repo. here, it's BookRepoName and repo_name. in Giten_site, it's Book.repo_name AND BookRepo.name.

No action warranted, yet.

There's also an assumption that the repo is in GITenberg. At some point this will be a state variable.