Two factors authentication

Closes #80 (closed) uses nexmo service for sms tokens

run ./manage.py two_factor_disable ${USERNAME} to disable two steps authentication for a specific user

smash/smash/local_settings.py.template

@@ -39,3 +39,7 @@ STATIC_ROOT = '/tmp/static'  # Warning! `/tmp` directory can be flushed in any m
 MEDIA_ROOT = '/tmp/media'  # Warning! `/tmp` directory can be flushed in any moment; use a persistent one, e.g. ~/tmp/media
 
 STATICFILES_STORAGE = 'django.contrib.staticfiles.storage.StaticFilesStorage'
+
+NEXMO_API_KEY = 'API_KEY'
+NEXMO_API_SECRET = 'API_SECRET'
+NEXMO_DEFAULT_FROM = 'Scheduling'  # the sender of the message (phone number or text)