- CoapChannelListener.java -> empty and unused (updated CoapClient and CoapServer accordingly)
modified
 - documentation (CoapResource)
 - cleanup (CoapResponseCode, CoapRequestCode, CoapPacketType )
 - added first test setting (InterfaceTest)
 - ResourceServer Interface now extends CoapServer (instead of being parallel)
 - ToDo's: removed already finished ToDo's, added some Fixme's for potential null pointer access