Game modes cleanup

- Fix some cases where modes were still referenced by number
- Replace most cases of mode range-comparison with is_out(), is_town(), and/or is_combat()

There could be some minor errors in the replacements.

src/game/boe.newgraph.cpp

@@ -642,7 +642,7 @@ void draw_shop_graphics(bool pressed,rectangle clip_area_rect) {
 		"Expensive","Exorbitant","Utterly Ridiculous"};
 	cItem base_item;
 	
-	if(overall_mode != 21) {
+	if(overall_mode != MODE_SHOPPING) {
 		return;
 	}