cluster shapefile exports - support grouped exports

[shawnlaffan]

Issue #161 added support for shapefile exports, but it is the entire tree. It would be useful to export grouped level data, as per the table_grouped export.

To do:

• Blog post - https://biodiverse-analysis-software.blogspot.com/2022/11/export-cluster-groups-to-shapefile.html

[shawnlaffan]

Ideally we would also dissolve the shapes, or generate multipart shapes. We would also use format like geopackage that supports longer field names.

Those can be separate issues, though.

[shawnlaffan]

Changes have been merged onto master branch

[shawnlaffan]

All tasks completed, so closing