Send notifications on mobile browser
As reported by @Majkl578
We currently do not send any notifications when using Gitter in a mobile browser.
Cause
Currently, public/js/router-mobile-app.js
doesn't import require('./components/user-notifications');
like other routers, public/js/router-app.js
We also should add the offline push notifications from the service worker, see https://gitlab.com/gitlab-org/gitter/webapp/blob/f583313453e3c186c0af3baafb415cc2e2bc8a00/public/js/router-app.js#L485