Increase number of parallel thumbnail download requests

lib/utils/file_util.dart

@@ -165,7 +165,7 @@ final Map<int, Future<io.File>> fileDownloadsInProgress =
 
 final _thumbnailQueue = LinkedHashMap<int, FileDownloadItem>();
 int _currentlyDownloading = 0;
-int kMaximumConcurrentDownloads = 32;
+int kMaximumConcurrentDownloads = 100;
 
 class FileDownloadItem {
   final File file;