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/InventoryUI.cs

@@ -0,0 +1,34 @@
+using UnityEngine;
+
+public class InventoryUI : MonoBehaviour {
+
+    public Transform itemsParent;
+    public GameObject inventoryUI;
+    private PlayerController playerController;
+    private InventorySlot[] slots;
+    
+    // Start is called before the first frame update
+    void Start() {
+        playerController = PlayerController.instance;
+        playerController.onItemChangedCallback += updateUI;
+
+        slots = itemsParent.GetComponentsInChildren<InventorySlot>();
+    }
+
+    // Update is called once per frame
+    void Update() {
+        if(Input.GetButtonDown("Inventory")) {
+            inventoryUI.SetActive(!inventoryUI.activeSelf);
+        }
+    }
+    
+    private void updateUI() {
+        for(int i = 0; i < slots.Length; i++) {
+            if(i < playerController.inventory.Count) {
+                // slots[i].addItem(playerController.inventory[i]); //TODO: dictionary "letztes" Item finden, Wie?!?!?!
+            } else {
+                slots[i].clearSlot();
+            }
+        }
+    }
+}