Fixed errors, tweaked stuff.

Fixed error where note 0 was actually played as some other note.
Fixed error where the first note on a human player's track was always
impure.
Set starting tracks to be empty, rather than have random content.
Replaced scroll functionality by keyboard with mouse controls - hold
RMB and move mouse left or right.
Set PlayController to start playing immediately, rather than wait for
space press. Not sure if that is the right thing, though.

Left to do:
Use German's graphics.
Make nicer sounds.
Ensure that the saved recording will be of a perfect take/performance.