core (xmpp): properly clean profile data in case of startConnection failure: - profile is now always removed from profiles_connecting - an exception is raised if client already exists only if client is connected. Otherwise, it's deleted (this allow to keep session open to e.g. modify settings in case of failure during connection)

# 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()