Added Drum Mode

Added a drum mode to your most recently updated code. It is accessible via the Add Track button while an instrument track is selected. It is a 4x4 grid made out of the 64 pad grid (no step sequencer). The octave buttons control what bank in the drum machine is selected. This view is really only applicable for the drum machine but it's a pretty useful view for it! I don't quite know why the grid is rainbow colored but that doesn't effect functionality and maybe makes it more fun!