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/GameMain.cs

@@ -0,0 +1,35 @@
+using System;
+using System.Diagnostics;
+using System.Reflection;
+using FarseerPhysics;
+using FarseerPhysics.Dynamics;
+using Barotrauma.Networking;
+using System.Collections.Generic;
+using Microsoft.Xna.Framework;
+
+namespace Barotrauma
+{
+    class GameMain
+    {
+        public static World World;
+
+        public static GameServer Server;
+
+        public static GameSession GameSession;
+
+        public static GameClient Client
+        {
+            get { return null; }
+        }
+
+        public static NetworkMember NetworkMember
+        {
+            get { return Server as NetworkMember; }
+        }
+
+        public static Screen EditMapScreen
+        {
+            get { return null; }
+        }
+    }
+}