Bug 1522 - No pointer or Status Bar indication of CTRL-click in waveform to move selection boundary

I also took the opportunity to modifier the Status Bar indications when in the TrackInfo.
1) We now mention ctrl click can select or deselect track.
2) If there is only one track, we don't now prompt about rearranging tracks, since you can't.
3) If you hover in a label track's VRuler (which is just a spacer so that things line up), you now don't get a message.

src/TrackPanel.h

@@ -291,6 +291,7 @@ class AUDACITY_DLL_API TrackPanel final : public OverlayPanel {
    // AS: Selection handling
    void SelectTrack(Track *track, bool selected, bool updateLastPicked = true);
    void SelectRangeOfTracks(Track *sTrack, Track *eTrack);
+   size_t GetTrackCount();
    size_t GetSelectedTrackCount();
    virtual void HandleSelect(wxMouseEvent & event);
    virtual void SelectionHandleDrag(wxMouseEvent &event, Track *pTrack);