plugin XEP-0050, adhoc D-Bus: Ad-Hoc improvment + remote media control: - "commands" namespace is now registered - added "do" and "getCommandElt" methods to XEP-0050 to run ad-hoc commands from backend - commands for a profile are now stored in client._XEP_0050_commands - Ad-Hoc D-Bus plugin can now be run without lxml or dbus (degraded) - use MPRIS to control media players - new adHocRemotesGet bridge method retrieve media players announced in all devices of the profile