Multi World NPCs + patch on Player interactions

Made NPCs now work properly on multiworld system. Solved multiple issues
regarding Player Shops not giving back items properly when owner exits.
Added restriction on changing channels at FM rooms, preventing shop
owner entering Cash Shop.

src/server/maps/FieldLimit.java

@@ -29,7 +29,7 @@ public enum FieldLimit {
     MOVEMENTSKILLS(0x02),
     SUMMON(0x04),
     DOOR(0x08),
-    CHANGECHANNEL(0x10),
+    CANNOTMIGRATE(0x10),    //change channel, town portal scroll, access cash shop, etc etc
     //NO_NOTES(0x20),
     CANNOTVIPROCK(0x40),
     CANNOTMINIGAME(0x80),

src/server/maps/HiredMerchant.java

@@ -57,7 +57,7 @@ public class HiredMerchant extends AbstractMapleMapObject {
     private String ownerName = "";
     private String description = "";
     private MapleCharacter[] visitors = new MapleCharacter[3];
-    private List<MaplePlayerShopItem> items = new LinkedList<>();
+    private final List<MaplePlayerShopItem> items = new LinkedList<>();
     private List<Pair<String, Byte>> messages = new LinkedList<>();
     private List<SoldItem> sold = new LinkedList<>();
     private boolean open;