Hello guys,
I wanted to add html5 web notifications when new alerts arrive. I needed this feature for my operation center team, so I learned the code a little bit and contributed :-)

I implemented a few things for this to happen:

1. SSE ("Server-sent event") application on server side, saving notifications in file and read new notifications when it changes.
2. client-side html5 notifications, just like gmail. with sound and icon.
3. I wanted the notifications to be role-based, so I implemented the method User::getRoles().
4. The notification data has to arrive from somewhere. I chose to rely on icinga2 notification scripts to do that.

so, In short, the notification flows this way:
icinag2 notification script --> sse.php --> events file
events file --> sse.php --> JS EventSource --> JS Notification

Hope that's clear. I'm sure you will want to do some changes, feel free.
I didn't thought about security here, so you probably will want to add a token here for adding a new event.

Edit : I looked at this more carefully and I think better base my notifications on the monitoring module notifications. I close this pull request and open a new one when I finish.