quick_frontend (widget, chat): implementation of new sync mechanism, first draft: QuickWidget implement base of sync mechanism with a sync property which can be overriden, and resync method which is called when resynchronisation is needed. When resync is required, chat widget get missing occupant and history elements A new callable argument can be used with historyPrint, when set it is called when history has been fully printed.

# XXX: the Monkey Patch is here and not in src/__init__ to avoir issues with pyjamas compilation
# TODO: remove this when changes are merged in Wokkel
from sat_tmp.wokkel import install
install()