Don't enforce grouping of attributes and relationships

[DavyLandman]

For this is incorrect:

entity Item {
	shelf: int
	product -> Product."Product.inventory"[1]
	picture: blob
}

while this is correct:

entity Item {
	shelf: int
	picture: blob
	product -> Product."Product.inventory"[1]
}

@davidediruscio suggested I raise an issue to remove this restriction.