Continue rationalisation of vector, trace and signal names.

Also add a little bit more code so user-defined signals can be edited
without resetting their properties.

Fixes https://gitlab.com/kicad/code/kicad/issues/14072

include/widgets/mathplot.h

@@ -264,7 +264,7 @@ public:
     /** Set layer name
      *  @param name Name, will be copied to internal class member
      */
-    void SetName( wxString name ) { m_name = name; }
+    virtual void SetName( wxString name ) { m_name = name; }
 
     /** Set layer font
      *  @param font Font, will be copied to internal class member