Added rudimentary support for HTML5 notifications in webkit

Implements prawnsalad#334.
The code is working but could probably be extended (always show notifications, etc). Since notifications can only be shown after the user enabled the notifications via a click event one has to enable the notifications in the settings first. I'm sorry about the formating, my hope is that you can just autoformat it so that it looks fine again.
I hope you like it and am looking forward to hearing your feedback!