implemented vertical "zooming" in the TimelineWidget and CurveView

This comes in the form of changing the vertical scale in the CurveView and
adjusting all track heights in the Timeline.

app/node/output/track/track.cpp

@@ -328,11 +328,21 @@ bool TrackOutput::IsTrack() const
   return true;
 }
 
+int TrackOutput::GetTrackHeightIncrement()
+{
+  return qApp->fontMetrics().height() / 2;
+}
+
 int TrackOutput::GetDefaultTrackHeight()
 {
   return qApp->fontMetrics().height() * 3;
 }
 
+int TrackOutput::GetTrackHeightMinimum()
+{
+  return qApp->fontMetrics().height() * 3 / 2;
+}
+
 QString TrackOutput::GetDefaultTrackName(TrackType type, int index)
 {
   // Starts tracks at 1 rather than 0

app/node/output/track/track.h

@@ -120,8 +120,12 @@ public:
 
   virtual bool IsTrack() const override;
 
+  static int GetTrackHeightIncrement();
+
   static int GetDefaultTrackHeight();
 
+  static int GetTrackHeightMinimum();
+
   static QString GetDefaultTrackName(TrackType type, int index);
 
   bool IsMuted() const;