Registration confirmation

New config setting 'confirm_registration' has been added. Default is false.

darvin_user:
    confirm_registration: true

if confirm_registration is true the new user account will not be enabled before he will not have confirmed it by code from email. The email message sends automatically, twig template is placed to DarvinUserBundle:User/email/confirmation:code.html.twig. Also the bundle has two new templates

1. @DarvinUser/User/confirmation/confirm_email_sent.html.twig - when user sends registration form
2. @DarvinUser/User/confirmation/confirmation_success.html.twig - when user click the confirmation link from email

if confirm_registration is false the behavior is previous.