Custom layouts

It might be nice to have custom form layouts (rather than 1 field per row).

We'd probably have to come up with some kind of JSON structure to represent the layout.

https://marmelab.com/react-admin/SimpleForm.html#complex-input-layout
https://marmelab.com/react-admin/TabbedForm.html
https://marmelab.com/react-admin/Fields.html#combining-two-fields

Also show layouts:
https://marmelab.com/react-admin/ShowTutorial.html#building-a-custom-layout
https://marmelab.com/react-admin/SimpleShowLayout.html#more-than-one-column
https://marmelab.com/react-admin/TabbedShowLayout.html

Alternative list?
https://marmelab.com/react-admin/InfiniteList.html