Pass associated_class to collection from show

Created by: stormmaster42

This fixes an issue where the embedded collection is using the parent's class to define i18n headers.

Example: Ressource order has_many order_items. Order dashboard declares order_items: Field::HasMany

When the show which includes the order_items association is rendered within the collection partial it uses the parent's resource (Order) instead of OrderItem to determine the header label default.

Not sure how to add a test for this behavior.