wip #300 - Redesigned Java API, some refactorings

While I understand this method name corresponds nicely with the name `save` allowing to write `toCassadra(....).save()`, the name alone is not descriptive at all. Also, the return type suggests it returns some options, and I would really not expect the actual save method would be on the options object. Try to think as someone who is using this API for the first time. 

Additionally, it is not consistent with the way how the corresponding Scala API works. I'm not particularly fond of having saveToCassandra with a million of optional parameters, as we have now (but this seems to be the Scala way of doing things).  I think this part of the API is important enough that we need to open a separate discussion for it (and add @helena).