Reducing usage of #if CLIENT / #elif SERVER

The server will implement some classes it probably shouldn't need because certain items or game states depend on them.

BarotraumaServer/Source/Networking/GameClient.cs

@@ -0,0 +1,19 @@
+using System;
+using Lidgren.Network;
+using Microsoft.Xna.Framework;
+using System.Collections.Generic;
+using System.IO;
+using System.Text;
+using System.ComponentModel;
+using System.Linq;
+
+namespace Barotrauma.Networking
+{
+    class GameClient : NetworkMember
+    {
+        public GameClient(string newName)
+        {
+            throw new Exception("Tried to create GameClient in dedicated server build");
+        }
+    }
+}