quick_frontend, primitivus: various fixes (MUC and cached signals): - actually call the cached signals, everything was there but the call was not done - display '[]' instead of '[None]' when group message coming from the room (no resource) - catch the exception when trying to delete an occupant who's not in the room - do not cache a "main resource" for MUC entities

# TODO: remove this when RSM and MAM are in wokkel
import wokkel
from sat.tmp.wokkel import delay as tmp_delay, pubsub as tmp_pubsub, rsm as tmp_rsm, mam as tmp_mam
wokkel.delay = tmp_delay
wokkel.pubsub = tmp_pubsub
wokkel.rsm = tmp_rsm
wokkel.mam = tmp_mam