Allow setting of scroll area explicitly

Defaults to scroll area being the parent element
of the sticky element, if not set.

app/templates/views/templates/choose.html

@@ -74,6 +74,7 @@
 
     {% if current_user.has_permissions('manage_templates') %}
       {% call form_wrapper(
+          class='sticky-scroll-area',
           module='template-folder-form',
           data_kwargs={'prev-state': templates_and_folders_form.op or None}
       ) %}