Velocity to Expression: Part I
 * Delete all references to velocity modifications
 * Replace them by expression
 * New Callback: onExpressionChanged(float value)
 * Callback onVelocityChanged not deleted because it could be of future use
 * Still not working, WIP
Velocity to Expression: Part II
 * Expression is now played live and saved in the resulting midi file.
 * Temp: in order to debug, the sequence is automatically saved when the Orchestrator is destroyed.
   The file's path is hardcoded as "tracks/saveFile.mid"
 * TorqueScript begin.cs: bugfix on the midi file name. Now it is automatically prefixed with "../tracks/"
 * modifObject.cs : onExpressionChanged implements onVelocityChanged