TMDM-7531: "Can't browse Roles from the PROVISIONING container in the Studio"

Fixes incorrect type used for lookup in system storage *and* for Role type.
Fixes incorrect type for lookup in getItemPKs.
Code clean up in ObjectPOJO (XtentisException is never thrown because a Map::get() on a non-null static final map is unlikely to cause any issue).
(https://jira.talendforge.org/browse/TMDM-7531)