added Inventory UI

added logic to inventory
 * it is very possible to be reworked in the near future
 * With
   - ScriptableItem
   - an own Inventory class maybe
   - if necessary no Dictionary anymore

Assets/Scripts/InventorySlot.cs

@@ -0,0 +1,30 @@
+using UnityEngine;
+using UnityEngine.UI;
+
+public class InventorySlot : MonoBehaviour {
+    public Image icon;
+    
+    private Item item;
+
+    public void addItem(Item newItem) {
+        item = newItem;
+
+        icon.sprite = item.defaultSprite;
+        icon.enabled = true;
+    }
+
+    public void clearSlot() {
+        item = null;
+        icon.sprite = null;
+        icon.enabled = false;
+    }
+
+    public void removeItem() {
+        PlayerController.instance.inventory.Remove(item);
+    }
+
+    public void useItem() {
+        //TODO: use item
+        Debug.Log("using " + item.displayName);
+    }
+}