Work in progress. Multi selection is working (using shift+click) but I've made a mistake somewhere because the default shift key behaviour is not working anymore.
This is not finished yet. More work than what I expected but the main part is done.
It will need a lot of testing... There is still a bug when activating a new extension
in development mode (ie. with python web server), I think it does not occur behind
a real web server.
Antoine Nguyen