improved Javadoc comments and added licence info

...g/springframework/samples/petclinic/model/BaseEntity.java

.../springframework/samples/petclinic/model/NamedEntity.java

...va/org/springframework/samples/petclinic/model/Owner.java

...a/org/springframework/samples/petclinic/model/Person.java

...java/org/springframework/samples/petclinic/model/Pet.java

.../org/springframework/samples/petclinic/model/PetType.java

...rg/springframework/samples/petclinic/model/Specialty.java

...java/org/springframework/samples/petclinic/model/Vet.java

...ava/org/springframework/samples/petclinic/model/Vets.java

...va/org/springframework/samples/petclinic/model/Visit.java

...ingframework/samples/petclinic/service/ClinicService.java

...ramework/samples/petclinic/service/ClinicServiceImpl.java

...ramework/samples/petclinic/util/CallMonitoringAspect.java

...g/springframework/samples/petclinic/util/EntityUtils.java