Backporting debhelper 12 is necessary to use disco as source for Tox
libmini isn't building, so I can't build utox. We could just stick with libtoxcore and qtox, and could then use cosmic instead and avoid debhelper 12.
Dropped filteraudio because it seems to be deprecated
Dropped toxic because I couldn't find an upstream source
Should the tox stuff go into the backports repository since it is from a later version of Ubuntu and (may) require debhelper to be backported, or should it go into the main repository because there is no older version in Trisquel 9?