Desktop notifications

[Kartones]

A possible enhancement is to setup a simple timer (a simple setinterval could do) to notify users (If they've gRanted consent/activated) with a simple alert() of tasks that have start time and that are going to happen.

This requires a few small new things:

• a mechanism to enable/disable desktop notifications
• exposing to JS on calendar page load all visible events with start date
• the js logic to check periodically and raise the alert()

I have my doubts of implementing this as means adding more javascript and currently already has a few things, and the initial goal was to avoid it as much as possible (impossible to achieve if we want a minimally decent UX). Maybe could be done after improving the javascript.