Refactor FormBuilder, replacing form_buffers with Arbre components.  See PR #3486 for discussion.
Remove form_buffer from filters form.
Fix active_admin_comments now that active_admin_form_for is a nested Arbre component.
Fix new password form, we can no longer break up active admin form in an ERB template.
Remove duplicate copy of test.
Formtastic + Arbre: will it blend?
Update documentation for forms including Arbre.