Song "Reminder" Notification

[Frick]

Ability to customize the song notification to appear at another point during the song. My personal thought is to provide two options: specify how far from the end of a song you'd like to be notified again (ex: 30 seconds from the end of the song), percentage of how far through the song (ex: notify me 50% through the song).

Note: don't forget to account for tracks less than the x seconds from end of song

[dotproto]

FYI, this is the main task I'd like to tackle in the near future.