Automation Point delete radius and size (#3902)

* Fix Automation Point delete radius. At lower zoom deleting would miss
automation points to delete and at higher zoom it would be too generous
and remove neighbouring points.

* Increase smallest Automation Point radius. For  visibility. The smallest
Automatin Point radius was tiny.

include/AutomationEditor.h

@@ -132,6 +132,7 @@ protected:
 	void getSelectedValues(timeMap & selected_values );
 
 	void drawLine( int x0, float y0, int x1, float y1 );
+	void removePoints( int x0, int x1 );
 
 protected slots:
 	void play();