Tell users when they're not in a supported location

[nickoneill]

Using 5 Calls from outside the US isn't well tested, we certainly don't return any reps but I'm not sure if we actually return an error or indicate that the app is not designed for use outside of the US. I do see some locations being reverse geocoded outside of the US so there are definitely users arriving from outside and probably having a confusing experience.

Let's display something nicer when users are outside a supported area when they find their location in the app.

• [ ] Return a json param from /v1/reps that indicates users are outside of the supported area @nickoneill
• [ ] Display information in the location picker that indicates the location is not supported, don't dismiss it immediately