Redefine the factories for track views and controls...

... non-intrusively in the Track suclasses, registering functions instead.

For each abstract factory function (of two), build a table of concrete factory
functions, paralleling the hierarchy of Track subclesses.  Dispatch using
runt time type information in the Track objects.

src/NoteTrack.h

@@ -222,10 +222,6 @@ public:
    int mVisibleChannels; // bit set of visible channels
 
    std::weak_ptr<StretchHandle> mStretchHandle;
-
-protected:
-   std::shared_ptr<TrackView> DoGetView() override;
-   std::shared_ptr<TrackControls> DoGetControls() override;
 };
 
 /// Data used to display a note track