core (xmpp): new networkEnabled() and networkDisabled() methods: those methods can be called by platform specific plugins when network is known to be (un)available. This way, connection attempts can be cancelled when no network is available, saving resources (notably battery on mobile devices), or attempts can be restarted immediately when network is known to be available again.

# 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()