Fix parent for new graph window, fix empty graphs are impossible to

selectively remove or edit, add associated signal to graphs so they
bring up the proper signal in the list on the right in the editing
window.

re/graphingwindow.h

@@ -26,6 +26,7 @@ public:
     QColor color;
     QCPGraph *ref;
     QString graphName;
+    DBC_SIGNAL *associatedSignal;
     //the below stuff is used for internal purposes only - code should be refactored so these can be private
     QVector<double> x, y;
     double xbias;