Fixed upload empty error

Due to a recent update, the jQuery-File-Upload widget changed the JSON format sent between the client and server thus causing an error. It also changed the value needed to grab the data with Javascript in index.html.erb (changed from "fileupload" to "blueimpFileupload").

https://github.com/blueimp/jQuery-File-Upload/issues/365#issuecomment-13859210
https://github.com/blueimp/jQuery-File-Upload/issues/2084#issuecomment-13923951