Transfer most available gtk-xt code to xoptions.c

Transfer most available gtk-xt code to xoptions.c

GenericPopUp and PopDown are grafted from gtk-xt into gtk2.
The version compiles, but segfaults before doing anything, with error
messages about unexpected cases in GenericPopup for Graph and PopUp Options
of the main board. The spin options need special treatment in GetWidgtText.