Add country code to log output

[mallorydxw]

At the moment we log "About to send SMS from %s to %s" before every SMS gets sent.

In order to make it easier for sysadmins writing scripts to check for suspicious things, we should add " [GB]" to the end of that which represents the country code of the recipient number.

There are PHP ports of Google's libphonenumber. That's probably our best bet.

Here's what I'm thinking:

1. Add an optional constant for the "local" region (maybe TWOFA_LOCAL_REGION)
2. Before logging, parse the number in the local context and get the 2-letter country code from the region code of the parsed number