Add PhoneNumber field

This changes the phone_number field to use a subclassed CharField
called PhoneNumberField which ensures a valid phone number is provided.
Various fixes

For tests, models and also the manager.
Environment settings

Optionally search for settings in os.environ if they don’t appear in
settings.
revert

This breaks, I changed the wrong manage.py!
Test updates.

Major updates changing tests to use run_tests.py. This also provides
django 1.6.1 functionality. NOTE: TESTS FAIL AT THE MOMENT.
Version bump

Version bump, as we’re making major changes to update for Django 1.6.1
PEP8
This currently breaks tests
This should fix travis ci
Whoops
spelling
Added twilio to requirements for tests.
Merge pull request #2 from phalt/phonenumber-field

Phonenumber field