component file sharing: comments metadata: new <comments> element is added to file metadata, it contains the URL to the comments virtual node and the count of comments (this way client knows if it make sense to request comments or not). Fixed triggers in plugin XEP-0264 (return value was missing). New trigger in plugin XEP-0329 to allow component to add metadata (used here for comments url).

# 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