Bug1669: Close and Menu buttons should never disappear...

... As they did with Ctrl+Shift+F, with a certain minimimum number of wave
tracks that depends on screen resolution.  On my Macbook, that was 13 tracks.

This bug was a consequence of James' TCP layout changes making buttons a little
taller plus my changes to hide any top controls for which there is not
sufficient height.

The fix makes the height of tracks after Ctrl+Shift+F a bit more (44 pixels
not 40) than in 2.1.3.

This fix also replaces some more "magic numbers" with calculation from
tabled data about TCP layout.

src/Menus.cpp

@@ -6391,9 +6391,7 @@ void AudacityProject::DoZoomFitV()
       return;
 
    height = height / count;
-
-   if (height < 40)
-      height = 40;
+   height = std::max( (int)TrackInfo::MinimumTrackHeight(), height );
 
    TrackListIterator iter2(GetTracks());
    t = iter2.First();

src/Track.cpp

@@ -33,6 +33,8 @@ and TimeTrack.
 
 #include "Experimental.h"
 
+#include "TrackPanel.h" // for TrackInfo
+
 #ifdef _MSC_VER
 //Disable truncation warnings
 #pragma warning( disable : 4786 )
@@ -130,11 +132,17 @@ void Track::SetOwner
 
 int Track::GetMinimizedHeight() const
 {
+   auto height = TrackInfo::MinimumTrackHeight();
+
    if (GetLink()) {
-      return 22;
+      auto halfHeight = height / 2;
+      if (GetLinked())
+         return halfHeight;
+      else
+         return height - halfHeight;
    }
 
-   return 44;
+   return height;
 }
 
 int Track::GetIndex() const

src/TrackPanel.cpp

@@ -1313,6 +1313,18 @@ std::pair< int, int > CalcBottomItemY
 
 }
 
+unsigned TrackInfo::MinimumTrackHeight()
+{
+   unsigned height = 0;
+   if (!commonTrackTCPLines.empty())
+      height += commonTrackTCPLines.front().height;
+   if (!commonTrackTCPBottomLines.empty())
+      height += commonTrackTCPBottomLines.front().height;
+   // + 1 prevents the top item from disappearing for want of enough space,
+   // according to the rules in HideTopItem.
+   return height + kTopMargin + kBottomMargin + 1;
+}
+
 bool TrackInfo::HideTopItem( const wxRect &rect, const wxRect &subRect,
                  int allowance ) {
    auto limit = CalcBottomItemY

src/TrackPanel.h

@@ -92,6 +92,8 @@ public:
    ~TrackInfo();
    void ReCreateSliders();
 
+   static unsigned MinimumTrackHeight();
+
    struct TCPLine;
 
    static void DrawItems