Integrates SignedForm with Active Admin.
This eliminates the need to explicitly permit all fields used in Active Admin forms in the generated Active Admin controllers.
gem 'signed_form-activeadmin'
Formtastic uses the check_box_tag helper and not check_box for boolean fields, so they are not caught by SignedForm.
This gem will thus sign every formtastic boolean input if SignedForm is used in the containing form and does not limit
this to Active Admin. If you use formtastic to add boolean fields to signed forms, you probably want them to be signed
as other types are automatically, so this should not be an issue.