I'd like MUCRoom to extend another interface (Result). The MUCRoom interface was recently changed to extend the Externalizable interface. As duplicate inheritance in Java isn't an option, I refactored MUCRoom to be an abstract class instead. The classes that implemented MUCRoom didn't seem to extend any other class, that's why I hope I can get away with this. :) Gato, do you agree? I'd like your feedback before I proceed.

git-svn-id: http://svn.igniterealtime.org/svn/repos/openfire/branches/rsm@9170 b35dd754-fafc-0310-a699-88a17e54d16e