Enhancement: Add image from URL

[mangtronix]

It would be cool if instead of uploading an image from local disk you could load the image into the AHD from a URL.

E.g. Parsons put up a page of pictures so it would be easier to copy and paste the picture URLs instead of having to save locally and then upload. http://portfolio.newschool.edu/dtparis/2014/09/01/168/

[huertanix]

This would be a bit tricky with Heroku's ephemeral filesystem, but there might be some S3 plugin or something for Paperclip that might make it possible; I'll look into it.