Improve actionform

This improves:

• Permission checks – now done on object level inside the form, if the action function has a permission property set
• Actions can return results (including HttpResponses, for e.g. export actions that generate a file download

added part::backend type::feature labels

assigned to @hansegucker

Looks fine.

enabled an automatic merge when the pipeline for a7e4aedd succeeds

merged

mentioned in commit fb090cde