Added several CallGS handlers.

GameServer/Server/CallGS/Handlers/Achievement/Achievement_OnAddSomeOne.cs

@@ -0,0 +1,13 @@
+namespace MikuSB.GameServer.Server.CallGS.Handlers.Achievement;
+
+// Client notifies the server that an achievement trigger condition was met. No response required.
+// param: {nType}
+[CallGSApi("Achievement_OnAddSomeOne")]
+public class Achievement_OnAddSomeOne : ICallGSHandler
+{
+    public Task Handle(Connection connection, string param, ushort seqNo)
+    {
+        // TODO: process achievement progress for the given nType
+        return Task.CompletedTask;
+    }
+}