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

common/servertalk.h

@@ -164,6 +164,7 @@
 #define ServerOP_ExpeditionLockoutDuration    0x0414
 #define ServerOP_ExpeditionSecondsRemaining   0x0415
 #define ServerOP_ExpeditionExpireWarning      0x0416
+#define ServerOP_ExpeditionChooseNewLeader    0x0417
 
 #define ServerOP_DzCharacterChange            0x0450
 #define ServerOP_DzRemoveAllCharacters        0x0451
@@ -2001,6 +2002,11 @@ struct ServerExpeditionID_Struct {
 	uint32 sender_instance_id;
 };
 
+struct ServerExpeditionLeaderID_Struct {
+	uint32 expedition_id;
+	uint32 leader_id;
+};
+
 struct ServerExpeditionMemberChange_Struct {
 	uint32 expedition_id;
 	uint32 sender_zone_id;