tools(xml_tools): fixed `<div>` unwrapping + added `parse` instance: `<div>` unwrapping could fail when a text node was a sibling of the top element (could easily happen ith a `\n` line feed added by an editor). This is fixed by filtering on IElement with `elements()`. A `parse` instance has been added as it is not necessary to create a new `ElementParser` each time that we want to parse something.

# 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()