[PATCH] Comply with new versions of the User (Mood|Tune|Activity) XEPs
The new versions of the User(Mood|Tune|Activity) XEPs specifies a stop command (which is an empty element). In Gajim a (back then) XEP compliant approach of retracting the PEP node was implemented. As "often" deleting and creating a node can be hard on the server the right way according to the new XEPs is to just publish the stop command. This patch replaces retracting with sending stop commands. (When Publishing Tunes is turned off it still retracts the node, because I assume that this means the node won't be recreated for some time.)
Milestone 0.12, because it is a rather non invasive change and will make the release comply with the XEP.