"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
- [x] prevent users from accessing pages besides '/' if they're not logged in
@dget I agree about using login_required... this was an attempt to implement it per https://flask-login.readthedocs.org/en/latest/#how-it-works. I think the specific piece you're referencing is for "If there are only certain times you need to require that your user is logged in," though. I'd prefer to get the @login_required decorator working. I'll take another stab at it.