Use work effort instead of total to compute revenue

total_effort contains the effort of the children but sum_tree needs only the
value of the work without the children.

review2931003

work.py

@@ -94,7 +94,7 @@ class Work:
 
         def getter(work):
             if work.list_price:
-                return work.list_price * Decimal(str(work.total_effort))
+                return work.list_price * Decimal(str(work.effort))
             else:
                 return Decimal(0)