core (memory): Sessions fixes: - avoid memory leak with forgotten _purgeSession in case of conflict: an exception is now raised instead - _purgeSession now cancel the timer if it was not done before - KeyError in profileGet is now explicitly raised throught a failure.Failure - use iterator to iterate session in ProfileSessions

# 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