Add row for nested/sub-albums

[v-marinkov]

Pigallery2 and Piwigo support them, whilst Immich and Librephotos don't.

[meichthys]

Contributions welcome. I'm not sure if want to support this myself. Some do also have a nested folder view which is very similar to albums (ie. Memories & Nextcloud)

[rodber]

Chevereto also supports nested albums.

[mhettig]

+1