Makes Airtight ECS. (#4351)

* Makes Airtight ECS.

* Remove atmos holdovers while at it!

Content.Server/Atmos/Commands/ShowAtmosCommand.cs

@@ -0,0 +1,34 @@
+using Content.Server.Administration;
+using Content.Server.Atmos.EntitySystems;
+using Content.Shared.Administration;
+using Robust.Server.Player;
+using Robust.Shared.Console;
+using Robust.Shared.GameObjects;
+
+namespace Content.Server.Atmos.Commands
+{
+    [AdminCommand(AdminFlags.Debug)]
+    public class ShowAtmos : IConsoleCommand
+    {
+        public string Command => "showatmos";
+        public string Description => "Toggles seeing atmos debug overlay.";
+        public string Help => $"Usage: {Command}";
+
+        public void Execute(IConsoleShell shell, string argStr, string[] args)
+        {
+            var player = shell.Player as IPlayerSession;
+            if (player == null)
+            {
+                shell.WriteLine("You must be a player to use this command.");
+                return;
+            }
+
+            var atmosDebug = EntitySystem.Get<AtmosDebugOverlaySystem>();
+            var enabled = atmosDebug.ToggleObserver(player);
+
+            shell.WriteLine(enabled
+                ? "Enabled the atmospherics debug overlay."
+                : "Disabled the atmospherics debug overlay.");
+        }
+    }
+}