Split lines now only show over middle third of track height.

This allows selection and clicking on split lines to merge clips to act independently.  It also means we don't need a portmanteau explanation in the status line, and the action to select up to a split line is simpler and easier to explain.

src/tracks/playabletrack/wavetrack/ui/CutlineHandle.cpp

@@ -88,6 +88,11 @@ namespace
             locRect.width = 11;
             locRect.y = rect.y;
             locRect.height = rect.height;
+            // Adjustment for split line, which only fills one third of track.
+            if( loc.typ != WaveTrackLocation::locationCutLine ){
+               locRect.y += rect.height/3;
+               locRect.height /= 3;
+            }
             if (locRect.Contains(event.m_x, event.m_y))
             {
                if (pCapturedTrackLocation)