Add basic teleportation and portals (#269)

* Add basic teleportation and portals

* Address PJB's feedback and minor cleanup

Content.Server/GameObjects/EntitySystems/PortalSystem.cs

@@ -0,0 +1,25 @@
+using Content.Server.GameObjects.Components.Movement;
+using JetBrains.Annotations;
+using Robust.Shared.GameObjects;
+using Robust.Shared.GameObjects.Systems;
+
+namespace Content.Server.GameObjects.EntitySystems
+{
+    [UsedImplicitly]
+    public class PortalSystem : EntitySystem
+    {
+        public override void Initialize()
+        {
+            EntityQuery = new TypeEntityQuery(typeof(ServerPortalComponent));
+        }
+
+        public override void Update(float frameTime)
+        {
+            foreach (var entity in RelevantEntities)
+            {
+                var comp = entity.GetComponent<ServerPortalComponent>();
+                comp.OnUpdate();
+            }
+        }
+    }
+}