New units in Necropolis. Discussion and selection between upgrades.

Both upgrades are quite good and practically comparable in terms of characteristics (ghosts have slightly higher initiative, while poltergeists are slightly faster and tougher), and their incorporeality helps them equally; the only choice is which ability to pick: they are usually not used very often, although casters still need to be attacked, and to steal arrows, it's enough to approach within movement range and use the ability. However, spirits still recover well from stolen mana, while poltergeists haven't figured out what to do with arrows yet. Perhaps, in the next patch, this aspect will be refined.