Try to add binary file support (doesn't work)

See :
* http://www.elasticsearch.org/guide/reference/mapping/attachment-type/
* https://github.com/elasticsearch/elasticsearch-mapper-attachments
*
https://github.com/scrutmydocs/scrutmydocs/blob/master/src/main/java/org/scrutmydocs/webapp/servlet/UploadServlet.java#L100