feat: Breaking change: support conjunctions of disjunctions of conjunctions when requesting attributes in any of the three supported session types

Instead of requesting several attributes, one can now request several groups of attributes. Within each such group, attributes belonging to the same credential type always come from the same credential instance. This affects all three session types, as in each of them attributes can be disclosed.

That is, irma.ServiceProviderRequest, irma.SignatureRequestorRequest, or irma.IdentityProviderRequest.
These structs contain new fields with which the requestor can configure the session
(they have in fact always been present in session request JWTs). Functions and endpoints
that start an IRMA session now support one of these; or an instance of irma.SessionRequest;
or JSON-serialized versions of any of those.

Co-authored-by: Confiks <confiks@scriptbase.org>

Co-authored-by: Confiks <confiks@scriptbase.org>

Co-authored-by: Confiks <confiks@scriptbase.org>

Co-authored-by: Confiks <confiks@scriptbase.org>

Co-authored-by: Confiks <confiks@scriptbase.org>