add Feature: Top Groups as sub folders

[finscn]

let the export images into some subfolders, folders are named with top-groups'name

[skjorn]

Sorry to take this long to review your request. I'll take a look as soon as possible. Thanks for your contribution in any case.

[Bahanix]

Works great! would be awesome to handle subfolder as well.

[skjorn]

Implemented to fully support the group hierarchy. It supersedes this. See the latest version.