Handled is leaf field also in UI

gms-ui/src/api/mock/data/groups.json

gms-ui/src/api/server/index.js

gms-ui/src/components/GroupsBreadcrumb.vue

gms-ui/src/components/GroupsPanel.vue

gms-ui/src/components/Main.vue

gms-ui/src/components/modals/AddGroupModal.vue

gms-ui/src/components/modals/RenameGroupModal.vue

gms-ui/src/store.js

...naf/ia2/gms/controller/BasicAuthWebServiceController.java

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

.../it/inaf/ia2/gms/controller/GroupsTabResponseBuilder.java

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

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

...ava/it/inaf/ia2/gms/model/request/RenameGroupRequest.java

...ava/it/inaf/ia2/gms/model/response/GroupsTabResponse.java

gms/src/main/java/it/inaf/ia2/gms/persistence/GroupsDAO.java

gms/src/main/java/it/inaf/ia2/gms/service/GroupsService.java

...ia2/gms/controller/BasicAuthWebServiceControllerTest.java

...inaf/ia2/gms/persistence/NestedGroupsIntegrationTest.java