Add Hibernate annotations to Purl
Add Hibernate annotations to Purl

In addition to adding Hibernate annotations, the field "PURL" was
tentatively renamed to "Identifier" to prevent confusion between
the name of its field and the name of the class.

Khyzad/PID-webservice,HawaiiStateDigitalArchives/PID-webservice,Khyzad/PID-webservice,HawaiiStateDigitalArchives/PID-webservice