Include 'linked' member for json-api collections

Include top-level 'linked' member when using JSON-API adapter. Needed to pass the hash to the elements in the collection, using the options hash worked, but I'm open to suggestions.  
Is the whitelist the list of associations that are always included? Where would that be specified, in the controller or the serializer?

I made it a String since that's what would be coming in from params[:include], but if whitelist is specified in controller/action, then I'll need to do something else.