Feature/fountain photos

Changes to API to get photo uploads working. This will have to be merged into master before CI passes for [the Add a Fountain feature on ios](https://github.com/jmoody/wetap-ios/pull/40).

Note that I've introduced webmock and vcr for stubbing network requests.

This branch is backwards compatible so I have no qualms about merging it in separate from the ios feature, but some day we may have backwards incompatible branches for the api/ios that have to be merged simultaneously - so keep that in the back of your mind.