This change adds the ability for hosting service and SCMTool backends to add their own JS views on top of the new repository form view. The base classes for these are pretty slim. The hosting service implementation only contains a small piece of functionality for choosing the display name for accounts, which has been moved out of the base RepositoryFormView. The SCMTool implementation is effectively a no-op. Testing Done: - Ran unit tests. - Used in conjunction with other changes to add some functionality for GitHub App-based connections.