pre-check templates/folders that were checked previously

(when rendering an error)

app/templates/views/templates/_template_list.html

@@ -17,6 +17,7 @@
           {{ unlabelled_checkbox(
             id='templates-or-folder-{}'.format(item.id),
             name='templates_and_folders',
+            data=templates_and_folders_form.is_selected(item.id),
             value=item.id,
           ) }}
         {% endif %}