Split levels, player, and hoop into separate files

I suppose this makes it a bit easier to navigate.
Move assets

Again, it feels a bit cleaner.
Update manifest
Use methods to get assets instead of classes

We could remove the Image, Sound, and Song classes now.
Laziness is the only thing keeping them around.
Version bump for 1.4.0

No changes in gameplay, just some heavily refactored internals.