Rejigging Item slots (#4933)

* itemslot overhaul

* remove "shared" prefix

* handle component shutdown

* comments, cleanup, tests

* comments and minor tweak

* rename ItemSlotManagerState

* fix swapping

* fix merge

* Add ItemSlot verb text override

* fix merge  (IEntity -> entityUid)

* Fix merge (LabelSystem)

* Fix merge (nuke disk)

* fix test

Content.Shared/Containers/ItemSlot/ItemSlotEvents.cs

@@ -1,23 +0,0 @@
-using Robust.Shared.GameObjects;
-
-namespace Content.Shared.Containers.ItemSlots
-{
-    /// <summary>
-    ///     Item was placed in or removed from one of the slots in <see cref="SharedItemSlotsComponent"/> 
-    /// </summary>
-    public class ItemSlotChangedEvent : EntityEventArgs
-    {
-        public SharedItemSlotsComponent SlotsComponent;
-        public string SlotName;
-        public ItemSlot Slot;
-        public readonly EntityUid? ContainedItem;
-
-        public ItemSlotChangedEvent(SharedItemSlotsComponent slotsComponent, string slotName, ItemSlot slot)
-        {
-            SlotsComponent = slotsComponent;
-            SlotName = slotName;
-            Slot = slot;
-            ContainedItem = slot.ContainerSlot.ContainedEntity?.Uid;
-        }
-    }
-}