Add Multiple Fields to Formidable Forms Drop Downs

For standard drop downs use:

https://gist.github.com/vfontjr/063296a79726e910aaf84d7f4f2bc81d#file-add_multiple_fields_dropdown-php

For dynamic fields (Formidable Pro only), use:

https://gist.github.com/vfontjr/063296a79726e910aaf84d7f4f2bc81d#file-add_multiple_fields_dynamic-php