introduce and setup jquer-fileupload-rails gem
enable to asyn submit form
update the key format
not to set return url
go to slide page after upload finished
unbind previous bindings to avoid uploading error file
fix i18n missing and error
handle upload result in slides.js
render human error messages to the client
Merge pull request #2 from 'Martin_288-add-progress-bar-to-upload-form'