fix couple silent bugs importing containers

1) we were setting OwnerHistory to the "elevation" attribute of SpatialElement (in BIMSpatialProperties.containers)
2) we were setting "elevation" attribute at all when SpatialElement doesn't have "elevation" attribute

Though those bugs were silent since PropertyGroup doesn't alarm when we add a completely new attribute to it.

src/blenderbim/blenderbim/tool/spatial.py

@@ -113,14 +113,12 @@ class Spatial(blenderbim.core.tool.Spatial):
             for element in rel.RelatedObjects:
                 related_objects.append((element, ifcopenshell.util.placement.get_storey_elevation(element)))
             related_objects = sorted(related_objects, key=lambda e: e[1])
-            for element in related_objects:
-                element = element[0]
+            for element, _ in related_objects:
                 new = props.containers.add()
                 new.name = element.Name or "Unnamed"
                 new.long_name = element.LongName or ""
                 new.has_decomposition = bool(element.IsDecomposedBy)
                 new.ifc_definition_id = element.id()
-                new.elevation = element[1]
 
     @classmethod
     def run_root_copy_class(cls, obj=None):