changes 30/08/2018

[nunomsfranco]

Changes done till 30/08/2018

• Thumbnails are currently disabled, can be enabled in setings.py.
• Upload and conversion are separated, messages are returned if file type needs to be converted or if can be uploaded without need of conversion (all of this can still be changed in settings.py).
• There is a new request for checking a file type.
• Checking the a task only returns the status and id, there is no return_url (if needed return may give the converted file name + extension).
• New request to download file, needs task id, returns file not a zip
• README.md was also updated with the new examples of request.