added png support for static presentations

Packages/vr.teachr.displays/Runtime/Scripts/PresentationController.cs

-using Codice.Client.BaseCommands.IssueTracker;
 using System;
 using System.IO;
 using TeachR.ApplicationManager;
 using TeachR.WebCommunication;
 using UnityEngine;
 using TeachR.StructureTree;
+using System.Linq;
 
 namespace TeachR.Displays
 {
@@ -12,6 +12,9 @@ namespace TeachR.Displays
     {
         public static Presentation Presentation { get; private set; }
         public static event Action OnLoad;
+        private static readonly string[] allowedFileFormats = { ".png", ".jpg" };
+        private static string folderPath;
+        private static string[] filePath;
 
         [RuntimeInitializeOnLoadMethod]
         private static void Init()
@@ -44,17 +47,16 @@ namespace TeachR.Displays
             else Debug.Log("No slides loaded yet");
         }
 
-
-        private static string folderPath;
-        private static string[] filePath;
-        // Look into themeFolder and load jpg-pictures to posters in classroom.
-        // If folder does not exist or is empty, no posters will be loaded.
         public static async void LoadPresentationOnThemeChange(string fromFolder)
         {
-            Debug.Log("ICH LEBE!");
             folderPath = Path.Combine(Application.streamingAssetsPath, "Config~", fromFolder, "presentation");
             if (!Directory.Exists(folderPath)) return;
-            filePath = Directory.GetFiles(folderPath, "*.jpg");// mehr dateiformate zulassen
+            //filePath = Directory.GetFiles(folderPath, "*.jpg");// mehr dateiformate zulassen
+
+            filePath = Directory.GetFiles(folderPath, "*.*", SearchOption.TopDirectoryOnly)
+                .Where(f => allowedFileFormats.Contains(Path.GetExtension(f)))
+                .ToArray();
+
             if (filePath.Length > 0)
             {
                Presentation = await Presentation.FromFiles(filePath);