add nickname support, try to fix campaign stage save

nksrv/LobbyServer/Msgs/User/SetNickname.cs

@@ -0,0 +1,26 @@
+using nksrv.Utils;
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace nksrv.LobbyServer.Msgs.User
+{
+    [PacketPath("/user/setnickname")]
+    public class SetNickname : LobbyMsgHandler
+    {
+        protected override async Task HandleAsync()
+        {
+            var req = await ReadData<ReqSetNickname>();
+            var user = GetUser();
+            user.Nickname = req.Nickname;
+
+            var response = new ResSetNickname();
+            response.Result = SetNicknameResult.NicknameOk;
+            response.Nickname = req.Nickname;
+                
+            WriteData(response);
+        }
+    }
+}