Tweak save_edit_row_form() of purchase batch view, to leverage handler

specifically this is to make use of handler's `update_row_quantity()` method,
when editing a row for ordering batches

docs/conf.py

@@ -109,6 +109,9 @@ pygments_style = 'sphinx'
 # If true, keep warnings as "system message" paragraphs in the built documents.
 #keep_warnings = False
 
+# Allow todo entries to show up.
+todo_include_todos = True
+
 
 # -- Options for HTML output ----------------------------------------------