Provide HTTP Builder for Groovy scripts

org.codehaus.groovy.modules.http-builder provides the commonly used
REST and HTTP builders for groovy scripts.
Fix broken delivery of email to supervisors

AbstractProvisioningService#sendCredentialsToSupervisor hadn't been
updated to the next-generation notification delivery, resulting in a
"java.lang.ClassCastException: java.lang.String cannot be cast to
org.openiam.idm.srvc.msg.ws.NotificationRequest"