Some "models" support

Hi, I've worked on adding some models object and data type support in swagger4j so here is what I've done.
Only parsing is supported and for swagger version 1.2 only. I did my best to respect the swagger specifications but I'm not an expert of it so I'd be glad if someone who knows them well could review this stuff.

So it adds data types support for primitives, arrays, void and ref. Complex type is only supported for the model objects (not for model object properties but most of the work is done so it shouldn't be hard to achieve).
The models objects are read (SwaggerReaderImpl) and added to the ApiDeclaration.

Regards,
Yann