[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
@vme-odoo , no need to make new method. it's ok to call version_info. see already we called version_info to check server connectivity https://github.com/odoo/odoo/blob/8.0/addons/web/static/src/js/chrome.js#L651