debian/control: adding dep on iceowl-extension > 31

The version 24.0.6 has a dependencie on version 31 or greater on
Thunderbird, adding a direct dependencie to iceowl-extension as Debian's
replacement for Ligthning.

Thanks to Paul van der Vlis for pointing this out.
linitan: bump up standards version to 3.9.6
debian/control: adding Christoph as uploader
document changes and release 24.0.6-3