Replace JCC with jnius

This branch changes from the JCC wrapper to the PyJnius project's reflection-based wrapper. We get rid of a native build step (though jnius requires Cython and a compiler), get reflection-based lookup (so much less casting) and simpler install/pypi upload.

Issues:
- [ ] `java.lang.Iterable` is not a Py `iterable`
- [ ] numbers (native) are not boxed for methods taking `Object`
- [ ] jnius setup.py fails in virtualenv's (patch to be sent upstream)