IPv6 support for Johanna

Added separator in session id to obtain IPv6 support.
Added unit tests to show the Ipv6 support.
Refactored code to use apache commons codec hex encoding, reducing code repetition.

I had researched on this one, too, when I first implemented the removed lines. I just didn't want to pick up a full external library, *just* to be able to hex-encode something. :-) Now that it's here anyways, go for it ...