python 3 updates

- Fix super() calls for python 3
- No need to inherit objects.
- No need for u at the start of strings
- Tidied up some brackets and f-strings too

web/pgadmin/tools/user_management/__init__.py

@@ -35,7 +35,7 @@ server_info = {}
 
 class UserManagementModule(PgAdminModule):
     """
-    class UserManagementModule(Object):
+    class UserManagementModule():
 
         It is a utility which inherits PgAdminModule
         class and define methods to load its own