plugin file download: meta plugin to handle file download: - first code in backend to use async/await Python syntax \o/ - plugin with file upload - URL schemes can be registered - `http` and `https` schemes are handled by default

# 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()