Long song = Blank canvas

[MarkMendell]

Canvases have a max size beyond which the browser renders them blank[0]. We currently make one long canvas with length relative to the length of the song, and a song around 6 minutes or more results in a canvas that's too long.

Fix this as part of the UI redesign since one solution will make the most sense given the new layout.

[0] http://stackoverflow.com/questions/6081483/maximum-size-of-a-canvas-element