Add ability to clone DBC signals. F2 will also do this from the

keyboard (very handy!)

dbc/dbcsignaleditor.h

@@ -27,6 +27,7 @@ private slots:
     void onCustomMenuSignals(QPoint);
     void onCustomMenuValues(QPoint);
     void addNewSignal();
+    void cloneSignal();
     void deleteCurrentSignal();
     void deleteCurrentValue();