Relationship model names and allow generation of relationships without instances

Hi,

My first pull request ever so apologies me if I'm doing it wrong!

I've updated to allow relationship names to reflect the actual class of the foreign key object in the case of the instance being derived from the model in the relationship instead of being of that class.

Also found it usefull to be able to generate the relationships without the actual foreign key objects in the case of having to do a big cut-and-paste job so have added a mode 'RELATED_OBJECT_EXCLUDE' to allow this.

Cheers,
Steve