Feature/file uploads

Completes https://app.asana.com/0/11169835259596/11950308787425.

Carrierwave is a really cool tool that seems to have a very practical feature set and straightforward implementation. I'd be interested to know how some of the other gems differ, since I'll probably be running into them in the wild.

Collaborators:
Super helpful Capybara cheat sheet (helped me figure out how to test the upload field)
https://gist.github.com/zhengjia/428105

Figured out the figaro gem, which has a documented executable that helps push environment vars to Heroku, requires the beta from github repo ... I wasted a lot of time trying to figure out why I kept getting figaro: command not found errors.
https://github.com/laserlemon/figaro