Add type validator objects to associations.

[tpendragon]

This allows for a good interaction point for adding additional type validations
to associations.

[mjgiarlo]

@terrellt One failing spec:

  1) ActiveFedora::Associations::Builder::HasAndBelongsToMany valid_options should eq [:class_name, :predicate, :before_add, :after_add, :before_remove, :after_remove, :inverse_of, :solr_page_size, :autosave]
     Failure/Error: it { should eq [:class_name, :predicate, :before_add, :after_add, :before_remove,

       expected: [:class_name, :predicate, :before_add, :after_add, :before_remove, :after_remove, :inverse_of, :solr_page_size, :autosave]
            got: [:class_name, :predicate, :type_validator, :before_add, :after_add, :before_remove, :after_remove, :inverse_of, :solr_page_size, :autosave]

       (compared using ==)

       Diff:
       @@ -1,5 +1,6 @@
        [:class_name,
         :predicate,
       + :type_validator,
         :before_add,
         :after_add,
         :before_remove,

[tpendragon]

@mjgiarlo Fixed.

[mjgiarlo]

👍