Repository based authorization

Still WIP
* Still ugly & need to figure out relationship between GithubRepositoryACL & GithubRequireOrganizationMembershipACL (subclasses, delegation, ???)
* No tests :(
* How to deal with src/main/java/com/cloudbees/jenkins/GitHubRepositoryName.java???
* Not working for private repos
* Is the scope hardcoding ok?