Normalizing phone number before app processes it in any way

Phone numbers in Mobile Commons requests always have the leading "1" international code. But when users input numbers on the web, they'll rarely add the international code. Since it's only the `createGame` function that has to deal with user-inputted data, it's only here that we'll try to normalize the phone numbers.

Closes https://github.com/DoSomething/ds-mdata-responder/issues/64
This is also not valid for international numbers. Length alone will not get you a valid number in many parts of the world.