Add support for Nested Documents in the Download Action

Implementation note: We should stop having Actions do the parsing of the URL and instead use the already parsed reference which can be retrieved with:

ResourceReference resourceReference = Utils.getComponent(ResourceReferenceManager.class).getResourceReference();
EntityResourceReference entityResource = (EntityResourceReference) resourceReference;
entityResource.getEntityReference()...

Note that ideally the Actions would need to be rewritten by implementing ResourceReferenceHandler<EntityResourceAction>.