InstrumentTrack: hide sound shaping widgets for single-streamed instruments

We currently don't apply envelopes/LFOs and filters to single-streamed
instruments, therefore hide the GUI.

include/InstrumentSoundShapingView.h

@@ -44,6 +44,8 @@ public:
 	InstrumentSoundShapingView( QWidget * _parent );
 	virtual ~InstrumentSoundShapingView();
 
+	void setFunctionsHidden( bool hidden );
+
 
 private:
 	virtual void modelChanged();