fixed some issues with reviving monsters

- fixed: Thing_Raise didn't properly set the spawn health.
- fixed: Thing_Raise did not the CanRaise state flag.
- fixed: Reviving a monster must also reset the damage type.
- fixed: Thing_Raise reset the actor after calling the raise state, but it should be before, just as the Archvile code is doing.
- consolidated some common code of Thing_Raise and Archvile resurrection into AActor methods.