Actions System + UI (#2710)

Co-authored-by: Vera Aguilera Puerto <6766154+Zumorica@users.noreply.github.com>

Content.Client/GameObjects/Components/HUD/Inventory/InventoryInterfaceController.cs

@@ -1,4 +1,5 @@
 using System;
+using System.Collections.Generic;
 using Content.Client.UserInterface;
 using Content.Shared.GameObjects.Components.Inventory;
 using Content.Shared.Input;
@@ -53,6 +54,10 @@ namespace Content.Client.GameObjects.Components.HUD.Inventory
         {
         }
 
+        /// <returns>the button controls associated with the
+        /// specified slot, if any. Empty if none.</returns>
+        public abstract IEnumerable<ItemSlotButton> GetItemSlotButtons(EquipmentSlotDefines.Slots slot);
+
         public virtual void AddToSlot(EquipmentSlotDefines.Slots slot, IEntity entity)
         {
         }