When app-templates are enabled, support resetting defaults only for the
app-templates.
Without this, it's not possible to reset app-template preferences
without also resetting the default preferences for all settings the
app-template does not override (used when there is no application
template loaded, and other app-templates).
These additional menu items are shown in menus when an app-template has
been loaded.
Address issue raised by T96427.
Reviewed By: mont29, brecht
Ref D16150
781d03efe4