Store composable data as JSON in configurable fields

Instead of nesting composable data in groups, composable data can now be stored
in named jsonb fields. See Page for an example.

Composable data fields are now configured directly, rather than via crud admin,
as these configurations are relevant to rendering as well as editing.

Prior versions of Koi had a bug where composable data was stored as a string
even if the field was a jsonb field. Upgrading will require a manual migration
to convert from strings to json. If you are upgrading from 3.1.2 or earlier, the
format of the composable_data field has not otherwise changed, but if you are
upgrading from 3.1.3 or later, you will need to split composable_data groups up
into separate fields.