Allow Ghost Monsters as a compatibility and MAPINFO option

[ReaperAA]

This is something that has been pointed out by some people in the past. Right now, the mappers have no control to set this option in MAPINFO and neither do the compatibility options in GZDoom's settings have this option. The only option in GZDoom compatibility settings related to this is "crushed monsters can be resurrected" but none for whether they are resurrected as normal enemies or ghosts.

The GZDoom devs have to manually add compatibility for such type of maps (like in the example):
viewtopic.php?f=7&t=48068

By allowing the option, GZDoom devs would no longer have to manually add compatibility for such type of wads in future.