Added url embedded object to experiment_type schema to allow external links for protocols
Added url embedded object to experiment_type schema to allow external links for protocols

hms-dbmi/fourfront,hms-dbmi/fourfront,hms-dbmi/fourfront,4dn-dcic/fourfront,hms-dbmi/fourfront,4dn-dcic/fourfront,hms-dbmi/fourfront,4dn-dcic/fourfront,4dn-dcic/fourfront