Add basic teleportation and portals (#269)

* Add basic teleportation and portals

* Address PJB's feedback and minor cleanup

Content.Client/GameObjects/Components/Movement/PortalVisualizer2D.cs

@@ -0,0 +1,55 @@
+using Content.Shared.GameObjects.Components.Movement;
+using JetBrains.Annotations;
+using Robust.Client.GameObjects;
+using Robust.Client.Interfaces.GameObjects.Components;
+using Robust.Shared.Interfaces.GameObjects;
+
+namespace Content.Client.GameObjects.Components.Movement
+{
+    [UsedImplicitly]
+    public class PortalVisualizer2D : AppearanceVisualizer
+    {
+        public override void InitializeEntity(IEntity entity)
+        {
+            base.InitializeEntity(entity);
+
+            var sprite = entity.GetComponent<ISpriteComponent>();
+
+            sprite.LayerMapSet(Layers.Portal, sprite.AddLayerState("portal-pending"));
+            sprite.LayerSetShader(Layers.Portal, "unshaded");
+
+        }
+
+        public override void OnChangeData(AppearanceComponent component)
+        {
+            base.OnChangeData(component);
+
+            var sprite = component.Owner.GetComponent<ISpriteComponent>();
+            if (component.TryGetData<PortalState>(PortalVisuals.State, out var state))
+            {
+                switch (state)
+                {
+                    case PortalState.Pending:
+                        sprite.LayerSetState(Layers.Portal, "portal-pending");
+                        break;
+                    // TODO: Spritework here?
+                    case PortalState.UnableToTeleport:
+                        sprite.LayerSetState(Layers.Portal, "portal-unconnected");
+                        break;
+                    case PortalState.RecentlyTeleported:
+                        sprite.LayerSetState(Layers.Portal, "portal-unconnected");
+                        break;
+                }
+            }
+            else
+            {
+                sprite.LayerSetState(Layers.Portal, "portal-pending");
+            }
+        }
+
+        enum Layers
+        {
+            Portal
+        }
+    }
+}