Can't start latest stable on ubuntu 20.04

Open3d does not seem to be related to this problem and it is discussed here).

Requiring xinerama extension on linux seems to be a very widespread problem. Qt says it is not a bug, as they document what X11 extensions are required, but since Ubuntu does not come with xinerama installed by default (maybe earlier ir did), this causing users some pain. Development of xinerama stopped more than a decade ago, and it seems that is being weeded out from more and more places, but its removal from Qt is only scheduled for Qt6. Until then, we either need to build our Qt with xinerama disabled or add a note to the Slicer installation instructions.