gabc Annotation header missing

[Nokel81]

When you go to download a score as a gabc the header lines "annotation" are not present, even though they are displayed as such in the render on the website.

For instance: https://gregobase.selapa.net/chant.php?id=132

I think that this information doesn't need to be manually added via the "edit" screen but could be added based on the "mode" and "usage" values.