Editing: accordions for expanding&collapsing sections of input fields#485

For example, any optional fields could be grouped to one section and hidden until expanded.

Same goes for fields that are somehow closely related to each other, there are use cases where certain fields clearly can be seen as a part of a group, so those groups of fields could be revealed one by one as chosen by the user.

This would be extremely useful especially when there are quite a large number of input fields in the editing form, so that it would not be just one long list.

Accordions should be possible to achieve using custom CSS but first there should at least be a way to define those field sections (groups) in the form.