Use idle events to update TrackPanel cursor...

... As when recording starts or stops, or the Tools button has changed, or
scrolling has changed the results of hit-test.

This reduces TrackPanel's intrusions into other code, including ProjectHistory.

Also for AdornedRulerPanel, which shares the base class CellularPanel

src/ProjectWindow.h

@@ -85,7 +85,6 @@ public:
    wxRect GetNormalizedWindowState() const { return mNormalizedWindowState;   }
 
    void RedrawProject(const bool bForceWaveTracks = false);
-   void RefreshCursor();
 
    void Zoom(double level);
    void ZoomInByFactor( double ZoomFactor );