First tests on LeObjects

em_test.py

 person = em.new_class(  'person',
                         display_name = 'Person',
                         help_text = 'Replace old person classtype',
-                        abstract = True,
+                        abstract = False,
                         group = base_group,
                         parents = em_object,
 )

lodel/leapi/leobject.py

         # Checks that uid is given
         for uid_name in self._uid:
             if uid_name not in kwargs:
-                raise AttributeError("Cannot instanciate a LeObject without it's identifier")
+                raise LeApiError("Cannot instanciate a LeObject without it's identifier")
             self.__datas[uid_name] = kwargs[uid_name]
             del(kwargs[uid_name])
             self.__initialized.append(uid_name)