core: replaced SkipHistory exception by a key in mess_data: SkipHistory was skipping all remaining triggers just to skip history, which is not the intented behaviour. Now history can be skipped by setting mess_data[u'history'] = C.HISTORY_SKIP, this way we won't skip importants triggers. When history is skipped, mess_data[u'extra'][u'history'] will be set to C.HISTORY_SKIP for frontends, so they can inform user that the message is not stored locally.

# FIXME: remove this when RSM and MAM are in wokkel
# XXX: the Monkey Patch is here and not in src/__init__ to avoir issues with pyjamas compilation
import wokkel
from sat.tmp.wokkel import pubsub as tmp_pubsub, rsm as tmp_rsm, mam as tmp_mam
wokkel.pubsub = tmp_pubsub
wokkel.rsm = tmp_rsm
wokkel.mam = tmp_mam