send notification on song start

Includes the title, DJ, and artist

two improvements that would be nice:

* Currently it asks for permission on login, since chrome requires you to ask for permission in response to a user input action (otherwise it just ignores your request). Ideally it seems like this would be a toggle-able action on the main screen, and it'd ask for permission the first time it's toggled on.
* Safari doesn't display the album art as the icon. I'm not sure if this is a content sniffing problem or what. Chrome shows it fine.