Storage system refactor & map init.

* Demonstrated map init working with guns, toolboxes, tool lockers.
* Refactored EntityStorage and ServerStorage to have a common interface.
* EntityStorage no longer uses ServerStorage PURELY for visuals.
  Use an appearance visualizer instead.

Content.Server/GameObjects/Components/Items/Storage/IStorageComponent.cs

@@ -0,0 +1,11 @@
+using Robust.Shared.Interfaces.GameObjects;
+
+namespace Content.Server.GameObjects.Components.Items.Storage
+{
+    public interface IStorageComponent
+    {
+        bool Remove(IEntity entity);
+        bool Insert(IEntity entity);
+        bool CanInsert(IEntity entity);
+    }
+}