SFI: add conversions for SfiSeq and visitables
SFI: add conversions for SfiSeq and visitables

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