Refactoring the base and source parts of BigML

Ah, i see that in fact this class doesn't represent a source as an object, but rather groups the functions needed to create and manipulate sources as independent dictionaries, right?  If that's the case, perhaps it could be called something like BigMLSourceHandler, or even just SourceHandler, and it can then derive very naturally from BaseBigML (or, as i was proposing to call it, BigMLConnection).