Bug 948341 - Convert Dialer to make use of the new Notification API

Usage of the new API maks the code cleaner, we only depends on
NotificationHelper for getIconURI. Since bug 890440 landed, when this
new API is used there is no more hack to remove notification, so we have
to handle it ourself:
 - we have to close the notification in the 'click' event handler that
   we install
 - when we load the call log, we check for any notification and close
   them.

The second point allows us to fix correctly bug 926318.