Album grouping: take2. This time using the existing Playlist::GraphicsItems so most of the model logic is kept intact. The model automatically groups items as needed, even when adding stuff one track at a time.

There are still issues with removeing individual items and dragging items around, as well as some graphical update glitches. Aside from this, the playlist is usable with grouped items. Oh, and dont mind the funky colors, I just needed something to clearly identify groups.

We should get our artist to look at how this can be made perrrrrty