Created a generic DataObject FormFactory interface that can be substituted in place of getCMSFields. Different FormFactories can depend on different kinds of context, such as
'Record' or 'Controller' - it's the responsibility of the code calling the factory to interpret and
supply this context.
The expected use-case is that rather than overriding getCMSFields(), developers can
change CMS UIs by manipulating the FormFactory associated with the given DataObject.
This is an experimental UI and may change before 4.0 stable is released.
