Facilitate an ApplicationRecord::AssociatedObject

[kaspth]

Lets you define an abstract to share any common behavior you may need among Associated Objects:

# app/models/application_record/associated_object.rb
class ApplicationRecord::AssociatedObject < ActiveRecord::AssociatedObject
end

I don't know what that common behavior may be yet, but I figure it's a good idea to expose.

[kaspth]

Hmm, this has issues with the extension block, where we may need to support that in the parent class — but we can't because it's not associated with an actual record class yet.

[kaspth]

And we're hitting the same issue with supporting Polymorphic Associated Objects.

[kaspth]

Has the same issues as #30 and #29, I think I still want this but not sure how to resolve it! So we close for now.