Use the convenience function XSetWMProperties to set size, input
and class hints, it also automatically sets the WM_CLIENT_MACHINE
(this one needed by _NET_WM_PID) and WM_LOCALE_NAME windows hints.

Plus we add support to the _NET_WM_PID atom which is needed by many
windows managers to correctly associate a SDL window to its process
and to related .desktop file and icon for the given host.