Gather all enchantment info into a single place

This also resolves several TODO notes about duplicate code and makes cPresetItem::ability an eEnchant

src/scenario/town.hpp

@@ -55,7 +55,8 @@ public:
 	class cItem { // formerly preset_item_type
 	public:
 		location loc;
-		short code,ability;
+		short code;
+		eEnchant ability;
 		int charges = -1;
 		bool always_there = false, property = false, contained = false;