Require authentication to see photos.

  * Users are created in the backend console, no UI for it.
  * Logout is not in the UI, must localStorage.clear()
  * Tests are pretty flaky until I figure out why
  * Two extra API routes so I could use respond_with, until I figure out why
Refactor page objects

  * Eliminate caching, just use instantiation
  * class methods are for navigation + action, instance methods are for action on current page