Data classes: file upload doesn't work

[pbres]

When creating or updating data item in Data classes section file upload is not working. After selecting the file to upload the UI gets updated but clicking "Confirm" does not upload the file.

Steps to reproduce:

• create dataClass with a field of type file
• deploy the socket to the instance
• go to Syncano dashboard -> Data classes
• click "Add Data Object"
• select a file to upload (png file in my case)
• click confirm
• File column is empty

[pbres]

@mkucharz I see this is still an issue, I can handle it if it's ok for you