Adds a Visualizer for the Gravity Generator (#2277)

* Adds Visualizer to GravityGenerator

* nullable

* snake bad

* -Reads layers from yaml
-Reads sprite states from yaml

* Fix GravityGridTest

Content.Shared/GameObjects/Components/Gravity/SharedGravityGeneratorComponent.cs

@@ -1,11 +1,11 @@
-using System;
+using System;
 using Robust.Shared.GameObjects;
 using Robust.Shared.GameObjects.Components.UserInterface;
 using Robust.Shared.Serialization;
 
 namespace Content.Shared.GameObjects.Components.Gravity
 {
-    public class SharedGravityGeneratorComponent: Component
+    public class SharedGravityGeneratorComponent : Component
     {
         public override string Name => "GravityGenerator";
 
@@ -54,4 +54,20 @@ namespace Content.Shared.GameObjects.Components.Gravity
             Key
         }
     }
+
+    [Serializable, NetSerializable]
+    public enum GravityGeneratorVisuals
+    {
+        State,
+        CoreVisible
+    }
+
+    [Serializable, NetSerializable]
+    public enum GravityGeneratorStatus
+    {
+        Broken,
+        Unpowered,
+        Off,
+        On
+    }
 }