Add better support for STI

Found this in my codebase:

``` rb
# Add STI support to Sync. This should be moved upstream.
module Sync
  class Resource
    def name
      model.class.try(:sync_model_name) ||
      model.class.model_name.to_s.underscore
    end
  end
end
```

It allows for telling STI models to use their base class's sync views.
