Data upload prototype [Not to be merged]

[hdoupe]

We've kicked around the idea of allowing users to upload their own dataset to PolicyBrain. This PR presents a prototype for allowing the user to do this. The purpose of doing this is:

1. proof of concept
   This is definitely possible. File upload capabilities similar to those used for the reform and assumptions files were used. Here's the input page:

and the output page (using the Tax-Calculator version of the CPS file):

2. identify potential challenges
   The goal is to not crash the server with a very large file. Using the file objects provided by Django and Flask are very helpful in this regard but the data has to be serialized when sent from Django to Flask and from Flask to Celery. I was semi-successfully able to pass a file-like object from Django to Flask but not from Flask to Celery. Celery only receives Pickle, JSON, or msgpack data. I haven't found a good way to to pass a file like object to Celery without using Pickle. I wound up just reading the data into memory and passing it around as a binary blob. This may be a viable approach, but we should be careful to not overwhelm the server.

[Also note that I ran all these tests locally. Hopefully, they hold up when deployed on servers. I plan to test this some time in the coming week.]