Refactors stacks to be fully ECS. (#4046)

Content.Client/GameObjects/EntitySystems/StackSystem.cs

@@ -0,0 +1,25 @@
+using Content.Client.GameObjects.Components;
+using Content.Shared.GameObjects.Components;
+using Content.Shared.GameObjects.EntitySystems;
+using JetBrains.Annotations;
+using Robust.Shared.GameObjects;
+
+namespace Content.Client.GameObjects.EntitySystems
+{
+    [UsedImplicitly]
+    public class StackSystem : SharedStackSystem
+    {
+        public override void Initialize()
+        {
+            base.Initialize();
+
+            SubscribeLocalEvent<StackComponent, StackCountChangedEvent>(OnStackCountChanged);
+        }
+
+        private void OnStackCountChanged(EntityUid uid, StackComponent component, StackCountChangedEvent args)
+        {
+            // Dirty the UI now that the stack count has changed.
+            component.DirtyUI();
+        }
+    }
+}