Cleaned up some warnings in bulk import/export extension

Added transactions to bulk import
Renamed beginTransaction to begin_transaction for naming consistency
Updated cron uploader to handle bulk import transactions

ext/transcode/main.php

@@ -182,7 +182,7 @@ class TranscodeImage extends Extension
                     $size_difference = 0;
                     foreach ($event->items as $image) {
                         try {
-                            $database->beginTransaction();
+                            $database->begin_transaction();
 
                             $before_size =  $image->filesize;