VZooming Changes

1: Guard zone 8 pixels wide in VRuler to reduce risk of accidental use.
2: VerticalZooming preference, for VRuler zooming, off by default,
3: Enabled Paul's right-click menu in VRuler with some extra
presets (x2 and x0.5)
4: Rearranged some messy code with lots of ifs to use a switch.

Also, with EXPERIMENTAL_HALF_WAVE defined we now get a
'half wave' option in the VRuler menu, that shows the wave top half.
We also use it in collapsed waves (and collapsing and restoring
a WaveTrack will get you back to normal zoom.

src/prefs/TracksBehaviorsPrefs.cpp

@@ -85,6 +85,9 @@ void TracksBehaviorsPrefs::PopulateOrExchange(ShuttleGui & S)
                     ScrollingPreferenceKey(),
                     ScrollingPreferenceDefault());
 #endif
+      S.TieCheckBox(_("Enable Vertical Zooming"),
+                    wxT("/GUI/VerticalZooming"),
+                    false);
 
       S.AddSpace(10);