Makes Airtight ECS. (#4351)

* Makes Airtight ECS.

* Remove atmos holdovers while at it!

Content.Server/Atmos/Commands/ListGasesCommand.cs

@@ -0,0 +1,27 @@
+using Content.Server.Administration;
+using Content.Server.Atmos.EntitySystems;
+using Content.Shared.Administration;
+using Robust.Shared.Console;
+using Robust.Shared.GameObjects;
+
+namespace Content.Server.Atmos.Commands
+{
+    [AdminCommand(AdminFlags.Debug)]
+    public class ListGasesCommand : IConsoleCommand
+    {
+        public string Command => "listgases";
+        public string Description => "Prints a list of gases and their indices.";
+        public string Help => "listgases";
+
+        public void Execute(IConsoleShell shell, string argStr, string[] args)
+        {
+            var atmosSystem = EntitySystem.Get<AtmosphereSystem>();
+
+            foreach (var gasPrototype in atmosSystem.Gases)
+            {
+                shell.WriteLine($"{gasPrototype.Name} ID: {gasPrototype.ID}");
+            }
+        }
+    }
+
+}