core: added imageCheck and imageResize methods: imageCheck will give a report on image, notably it will tell if it's too big and needs to be resized before a transfer. imageResize will create a new image with the requested size and return a path to it.

# 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()