Paperclip file uploading (for the API)

Now Sparks have a new attribute, "file," which allows files to be uploaded and saved to Amazon S3.

Behold, after much pain on the parts of me and Aqeel, [the first image on STEAMnet](http://s3.amazonaws.com/steamnet/sparks/files/000/000/023/original/1374087685765.jpg?1374444023). It's definitely an inspiration spark.