Replace `DefaultAccountModelFactory` with `ResourceToMapConverter`

[lhazlewood]

ResourceToMapConverter will be included when #929 is complete. RTMC is a more generic (non-MVC-specific) class that can be used generically as a simple function, while the AccountModelFactory is coupled to MVC.

Implementation note: For backwards compatible reasons, we won't be able to delete DefaultAccountModelFactory - just deprecate it to be removed in an eventual 2.0 future release. The refactoring still needs to assume the AccountModelFactory interface, but the new implementation of that interface should just delegate to a ResourceToMapConverter instance.

This issue cannot be accomplished before 1.1.0 because it relies on code intended for a 1.1.0 release.