Update UploadFormat.php

The modification permits to define generic mime types with the following declaration:
UploadFormat::$allowedMimeTypes = array("audio/*", "video/*", "image/*");

This is consistent with the "accept" attribute of the HTML input tag.
&lt;input type="file" accept="audio/*|video/*|image/*|MIME_type" /&gt;

Regards,

Olivier