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/TimeTrack.h

@@ -113,10 +113,6 @@ private:
    Track::Holder Clone() const override;
 
    friend class TrackFactory;
-
-protected:
-   std::shared_ptr<TrackView> DoGetView() override;
-   std::shared_ptr<TrackControls> DoGetControls() override;
 };