Fixes to WampCra Implementation

Hi, I realized that I had a bug on my WampCra implementation, when using auth extra arguments:
AuthExtra objects where passed thru a variable argument, and that in Java is an array, regardles if you pass only one object, it always wraps it in an array. So jackson would encode that not in a Json but into a Json array, and therefore, the python server would receive a list, instead of a dictionary, and auth extra is expected to be a dict.

So, to solve it, I extended the interface, making two different functions, one for authentication with extras and one without. And also I implemented the interface of course.

Well that's all, regards,
Alejandro.