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/Fill/ToolboxElectricalFillComponent.cs

@@ -0,0 +1,38 @@
+using System;
+using Robust.Server.Interfaces.GameObjects;
+using Robust.Shared.GameObjects;
+using Robust.Shared.Interfaces.GameObjects;
+using Robust.Shared.IoC;
+using Robust.Shared.Maths;
+
+namespace Content.Server.GameObjects.Components.Items.Storage.Fill
+{
+    internal sealed class ToolboxElectricalFillComponent : Component, IMapInit
+    {
+        public override string Name => "ToolboxElectricalFill";
+
+#pragma warning disable 649
+        [Dependency] private readonly IEntityManager _entityManager;
+#pragma warning restore 649
+
+        void IMapInit.MapInit()
+        {
+            var storage = Owner.GetComponent<IStorageComponent>();
+            var random = new Random(DateTime.Now.GetHashCode() ^ Owner.Uid.GetHashCode());
+
+            void Spawn(string prototype)
+            {
+                storage.Insert(_entityManager.SpawnEntity(prototype));
+            }
+
+            Spawn("Screwdriver");
+            Spawn("Crowbar");
+            Spawn("Wirecutter");
+            Spawn("CableStack");
+            Spawn("CableStack");
+
+            // 5% chance for a pair of fancy insulated gloves, else just a third cable coil.
+            Spawn(random.Prob(0.05f) ? "YellowGloves" : "CableStack");
+        }
+    }
+}