This reverts commit 53d82e48.

This reverts merge request !271

This MR includes:
- Create group types
- Edit group types
- Delete group types
- Connect group type to groups

This MR includes:
- List additional fields
- Create additional fields
- Edit additional fields
- Delete additional fields
- Add fields to group

Can change preferences for sites, persons and groups

- Add ExtensibleForm
- Allow strings for layout nodes
- Add layouts

This finalises the migration to the black code style by applying double-quotes.