So try to set size to full "screen" size. most window managers
will ignore this however unless _NET_WM_FULLSCREEN_MONITORS is
set, Under gtk3 we can use gdk_window_set_fullscreen_mode to
do that. Its effectively impractical for LibreOffice to itself
calculate the right parameters for _NET_WM_FULLSCREEN_MONITORS
as far as I can see

Change-Id: Ia725f21048bfcec3dbf1478b4303ccd9cfec0b36