Make language restart a Promise

Something like: 
``` 
set_language: function(user, contact) {
        if (contact.extra.language_choice !== null) {
            return user.set_lang(contact.extra.language_choice);
        } else {
          return Q();
        }
    }

self.states.add('question_1_friendliness', function(name) {
            go.utils.set_language(self.im.user, self.contact)
                .then(function(){
                    return new ChoiceState(name, {
                        question: $('Welcome. When you signed up, were staff at the facility friendly & helpful?'),

                        choices: [
                            new Choice('very-satisfied', $('Very Satisfied')),
                            new Choice('satisfied', $('Satisfied')),
                            new Choice('not-satisfied', $('Not Satisfied')),
                            new Choice('very-unsatisfied', $('Very unsatisfied'))
                        ],

                        next: 'question_2_waiting_times_feel'
                    });
                });
        });

```