Thumbnail URL for uploaded images

To display preview in template-download, the thumbnail URL must be set.
this.thumbnailUrl = baseUrl + '/thumnail/' + encodeURIComponent(this.name);

If imageMagik is not available, there will be no thumbnail.
A workaround is to change <img src="{%=file.thumbnailUrl%}"> to  <img src="{%=file.url%}" class="img-responsive">