Let world handle expedition leader changes

This should eliminate race conditions caused by zones trying to set
a leader when members in different zones quit at the same time

Zone still detects when leader goes offline to trigger a change
since it's easier than having world process expedition member status
updates and perform expedition lookups

world/expedition_database.h

@@ -34,6 +34,7 @@ namespace ExpeditionDatabase
 	void PurgeExpiredExpeditions();
 	void PurgeExpiredCharacterLockouts();
 	void UpdateDzDuration(uint16_t instance_id, uint32_t new_duration);
+	void UpdateLeaderID(uint32_t expedition_id, uint32_t leader_id);
 };
 
 #endif