Custom shapefile support

[vmikk]

Hello!

Currently, Biodiverse only supports plotting rectangular grid cells in the GUI. I would like to propose extending the plotting functionality and adding support for custom shapefiles.

For instance, Uber's H3 hexagonal grid cells are becoming more popular in the field of spatial data analysis, and I believe this would be a useful addition for users who work with this type of data. This would allow users to visualize and analyze data using non-rectangular grid cells easily.

[shawnlaffan]

The recent rebuild of the canvas system makes this much more feasible but it will still take a few days to implement. Hence pushing back to 5.1 rather than delay 5.0 any further.