Finish support of generalized status effects (probably)

- Negative dumbfounding increases effective magic skills; works on monsters too (though it already did)
- Martyr's Shield no longer permanent on monsters
- Invisible status effect works on monsters (same as permanent invisibility)
- Poisoned weapon status effect works on monsters (adds poison to their first melee attack)
- Restore Mind spell no longer removes negative dumbfounding
- Invulnerability status effect works on monsters (same as permanent invulnerability, and stacks with it)
- Magic resistance status effect works on monsters (halves fire/cold damage)
- Negative magic resistance doubles magic/cold damage (both on PCs and monsters)

src/boe.graphutil.cpp

@@ -186,7 +186,7 @@ void draw_monsters() {
 			}
 	if(is_town() || is_combat()) {
 		for(i = 0; i < univ.town.monst.size(); i++)
-			if(univ.town.monst[i].active != 0 && !univ.town.monst[i].invisible)
+			if(univ.town.monst[i].active != 0 && !univ.town.monst[i].invisible && univ.town.monst[i].status[eStatus::INVISIBLE] <= 0)
 				if(point_onscreen(center,univ.town.monst[i].cur_loc) && party_can_see_monst(i)) {
 					check_if_monst_seen(univ.town.monst[i].number, univ.town.monst[i].cur_loc);
 					where_draw.x = univ.town.monst[i].cur_loc.x - center.x + 4;