Implement machine linking (#1784)

* Implement machine linking

* Cleanup and rename Signals

* Implement signal button

* Add machine linking signal mapping

* Fix signallink command help

* Add localization to signal linking and allow infinite range

* Add feedback for when a transmitter is not connected to any receivers

Refactor PopupMessage to use the entity extension
Refactor dependencies to not have to disable warnings

Content.Server/GameObjects/Components/MachineLinking/SignalLinkerComponent.cs

@@ -0,0 +1,21 @@
+using Robust.Shared.GameObjects;
+using Robust.Shared.ViewVariables;
+
+namespace Content.Server.GameObjects.Components.MachineLinking
+{
+    [RegisterComponent]
+    public class SignalLinkerComponent : Component
+    {
+        public override string Name => "SignalLinker";
+
+        [ViewVariables]
+        public SignalTransmitterComponent Link { get; set; }
+
+        public override void Initialize()
+        {
+            base.Initialize();
+
+            Link = null;
+        }
+    }
+}