Feature Request: Add ability to edit polygons

[james-h-dt]

Great tool Matt, good work fella.

Would be great if custom polygon objects could be edited.

For example: double-clicking an existing polygon opens it in an edit view; shows the current points; allows existing points to be dragged to new locations; allows new points to be added; allows existing points to be removed/dissolved & the polygon auto-reshapes itself to handle the removal.

Benefits: Feature would allow existing shapes to be re-visited and tuned. Also would allow incorrect shapes to be reworked, without having to start again.