upgrade Javassist to a newer version

The javassist version we currently use (3.11.0.GA) creates permgenspace leaks and looses the configured MethodHandler on de-serialization.

We should upgrade to a new version if available.

The library currently has 2 problems

1.) serialization doesn't work (looses the MethodHandler)

2.) the internal cache is broken, so we should disable it. This has no impact on OWB, since we already cache generated proxy classes ourselfs.