Bump iiif-net and use exposed options with iiif-net derrived collections

[p-kaczynski]

Essentially we use JsonSerializerSettings used by iiif-net, as it provides (now) working converters in correct order to handle all the weirdness of the iiif collections. Additionally, as the iiif-net package has no idea about a FlatCollection, so we provide it in serialization context.

It's not pretty but kinda "reality of working with json dot net"

60 tests passing on my local env.