Added PermissionsController and search user functionality

gms/src/main/java/it/inaf/ia2/gms/authn/SessionData.java

...ain/java/it/inaf/ia2/gms/controller/GroupsController.java

...ava/it/inaf/ia2/gms/controller/PermissionsController.java

...main/java/it/inaf/ia2/gms/controller/UsersController.java

gms/src/main/java/it/inaf/ia2/gms/model/Identity.java

gms/src/main/java/it/inaf/ia2/gms/model/IdentityType.java

gms/src/main/java/it/inaf/ia2/gms/model/RapUser.java

...va/it/inaf/ia2/gms/persistence/PermissionsRepository.java

gms/src/main/java/it/inaf/ia2/gms/rap/RapClient.java

...main/java/it/inaf/ia2/gms/service/PermissionsService.java

...af/ia2/gms/service/PermissionsServiceIntegrationTest.java