"Who Am I?" – log in with Personas

Pivotal Tracker ticket [#75075362](https://www.pivotaltracker.com/story/show/75075362), "As a City stakeholder, I want users of this system to have to log in before they can see any sensitive data."

Known TODOs:
- [ ] write tests
- [ ] resolve merge conflicts with master
- [ ] prevent users from accessing pages besides '/' if they're not logged in