MISC: Dockerfile-bionic: upgrade dependencies remove old packages
MISC: Dockerfile-bionic: upgrade dependencies remove old packages

* Upgrade pandoc to 2.9
* Upgrade fluidsynth to 2.0.9
* Remove gnomecanvas, pango, gtk2
* Add libgtk-3 for newer electron versions
* Add gettext, needed by the build tools
* Keep libgdk-pixbuf2.0-dev until we replace gdk-pixbuf-csource

Signed-off-by: Tim Janik <6ec6ff229c4e1c5bbd5933ee92e6c5832ff023bb@gnu.org>

tim-janik/beast,swesterfeld/beast,swesterfeld/beast,tim-janik/beast,tim-janik/beast,swesterfeld/beast,swesterfeld/beast,tim-janik/beast,swesterfeld/beast,swesterfeld/beast,swesterfeld/beast,tim-janik/beast,tim-janik/beast,tim-janik/beast