Mailchimp actions on user

To avoid creating false mailchimp list entries while in development and during testing , a newly confirmed user should only be added to the mailchimp subscriber list in production.

``` ruby
def add_user_to_mailchimp
     return unless ENV['RAILS_ENV']=='production'
     :
end

def remove_user_from_mailchimp
    return unless ENV['RAILS_ENV']=='production'
    :
end
```
