Implement lazy image loading (copied from freefall reader)

Services/FileDownloader.cs

@@ -0,0 +1,32 @@
+namespace QuestReader.Services;
+
+public class FileDownloader
+{
+    public static async Task DownloadList(string basePath, Uri baseAssetsUrl, IEnumerable<string> files)
+    {
+        if (!Directory.Exists(Path.Join(basePath, "assets")))
+            Directory.CreateDirectory(Path.Join(basePath, "assets"));
+
+        var downloadTasks = new List<Task>();
+
+        using (var client = new HttpClient()) {
+            client.BaseAddress = baseAssetsUrl;
+            Console.Out.WriteLine($"Downloading missing files...");
+
+            await Task.WhenAll(
+                files
+                    .Where(file => !File.Exists(Path.Join(basePath, "assets", file)))
+                    .Select(file => client.GetStreamAsync(file).ContinueWith(async (stream) => {
+                            Console.Out.WriteLine($"Downloading {file}");
+                            using var fileWrite = File.OpenWrite(Path.Join(basePath, "assets", file));
+                            await (await stream).CopyToAsync(fileWrite);
+                            stream.Dispose();
+                            fileWrite.Dispose();
+                        })
+                    )
+                    .ToList()
+            );
+            Console.Out.WriteLine($"All files done");
+        }
+    }
+}