Feature/api auth

Require API authentication to create fountains. Also adds login UI to be embedded in the mobile client.

This is a backwards incompatible change - **deploying this will break existing clients ability to create fountains**.

https://www.pivotaltracker.com/story/show/67121414
It's coming back to me slowly. This was a devise hook that I found to run every time before a user entered into a "authenticatable" flow. It looks like the :before_save hook should be sufficient to do the trick here.