Core: Improve constant channel handling

- Implement area restrictions
  - Disable constant channels in arenas
  - Implement city requirement
- Implement global constant channels
- Fix some packets

--HG--
branch : trunk

src/server/game/Entities/Player/Player.h

@@ -1878,6 +1878,8 @@ class Player : public Unit, public GridObject<Player>
 
         void SetMovement(PlayerMovementType pType);
 
+        bool CanJoinConstantChannelInZone(ChatChannelsEntry const* channel, AreaTableEntry const* zone);
+
         void JoinedChannel(Channel *c);
         void LeftChannel(Channel *c);
         void CleanupChannels();