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.

Ran unit tests.
Used in conjunction with other changes to add some functionality for

  GitHub App-based connections.