[IMP] web : Add Indicator to notify user when connection get lost

Task: https://www.odoo.com/web#id=9963&view_type=form&model=project.task&menu_id=3942&action=327
Pad: https://pad.odoo.com/p/r.ZzhDtxgl8FMoYhXu
Does not seems a good idea, this function is call after each 2 seconds, doesn't it seems bad to do RPC after 2 seconds continuous ?
I proposed better solution in pad