Added setting origin/link converters with attributes. Added support for indexed origin/link. Added JsonLinkedContext.RememberLinkScoped to manually walk origins.
Added base JSON serializers: JsonConverter<T>, JsonJObjectConverter<T>, JsonOriginConverter<T>.
JsonLinkedContractResolver now preserves already set converters.
Removed IIdentifiable<string> implementation by values from requirements of link providers.
Removed constructors from owned collections which allow specifying contained list. Simplified JsonOriginConverter<T> code.