Gksu removed from Ubuntu 18.04 and Debian Testing/Sid

[rolandoislas]

• Update the installer to check for pkexec instead of gksu
• Update the desktop file to use the command pkexec env DISPLAY=$DISPLAY XAUTHORITY=$XAUTHORITY /usr/local/bin/drc-sim-backend

[jleacox]

Found this site which forces the install of gksu: https://ubuntu-mate.community/t/for-anyone-who-still-needs-or-wants-gksu/16744 Not a fix but a way around it. Seems to need this module as well: https://askubuntu.com/questions/342202/failed-to-load-module-canberra-gtk-module-but-already-installed