Abstract idea of Song instead of pure file management

[Casey Link]

I've started a feature proposal on the wiki:
http://amarok.kde.org/wiki/Proposals/Song_Abstraction

If you don't mind Jud, I used quite a bit of your text in the various
descriptions.

I'll be adding to the technical part of the proposal (what this will
actually affect in Amarok's internals) over the next couple days.

All: Feel free to comment, add, edit, etc

Casey