Add "clear track" option, fix copying of tracks from song ed -> bb ed

- Tracks copied from song->bb will no longer be unusable
- Since doing this required creating a "delete TCOs from track" function, I also added the option to trackops menu to clear a track
Fix #757

include/bb_editor.h

@@ -23,8 +23,8 @@
  */
 
 
-#ifndef _BB_EDITOR_H
-#define _BB_EDITOR_H
+#ifndef BB_EDITOR_H
+#define BB_EDITOR_H
 
 #include "TrackContainerView.h"
 
@@ -45,6 +45,8 @@ public:
 	{
 		return( true );
 	}
+	
+	virtual void dropEvent( QDropEvent * _de );
 
 	void removeBBView( int _bb );
 

include/track.h

@@ -349,6 +349,7 @@ private slots:
 	void updateMenu();
 	void recordingOn();
 	void recordingOff();
+	void clearTrack();
 
 private:
 	static QPixmap * s_grip;
@@ -431,6 +432,7 @@ public:
 	trackContentObject * addTCO( trackContentObject * _tco );
 	void removeTCO( trackContentObject * _tco );
 	// -------------------------------------------------------
+	void deleteTCOs();
 
 	int numOfTCOs();
 	trackContentObject * getTCO( int _tco_num );