Fix: Retain composite tie on C++ side so composite ties can be undone.
Fix typo, tiny bit of comment/cleanup
In-progress: growth rate plot point labelling
Add GrowthRatePlotCanvas class, move growth rate data and handling into this class where it belongs (out of CompositePanel and BetterLegendPlotCanvas)
Updated comment explaining contents of HoleData super-list/tuple fest
Display hole+core and growth rate in Growth Plot status bar; auto-range Growth Plot to include cores with any portion visible in composite area (using composite area start/end depth for range omits visible cores' data in Growth Plot as offsets grow larger deeper in composited holes)