Switched notification api

WebkitNotifications is not available for extentions.
Switched to Chrome Notifications
https://developer.chrome.com/apps/notifications

fixes #3
Added missing files.

These files are needed "on disk" for the extention to be able to display avatars in notifications.
Merge pull request #5 from tormodh/3-change-notification-api

Changed notification API. -- thx tormod!