Consider “Request” as a separate entity from eli:LegalExpression

Why? To support the use case that when a legislation is updated and this does not impact the request, the request can be also associated with that updated legislation.

In the original model the Request and its Legal Expression shared the same identity as a Request was encoded as a subclass of a Legal Expression. We propose to consider them as separate entities each with their own lifecycle, but closely related.  This enables to support, for instance, the use case that when a legislation is updated and this does not impact the request, the request can be also associated with that updated legislation.