plugin XEP-0060, tmp(wokkel.rsm): small refactoring: - don't use getRSMResponse anymore: rsm.PubSubClient use a different signature which return items and RSMResponse, this is better than the previous method as if the requested don't call getRSMResponse, there is no memory leak anymore. - use RSMResponse directly instead of using ext_data, as other extension (like MAM) will be probably be managed with an other workflow - don't do a useless deep copy of pubsub.PubSubRequest._parameters on each instance anymore - RSMResponse.parse do now manage parsing of <set/> element directly