*Background:* Users often misspell there emails and passwords and can't login a 2d time
*Studio Updates:* None.
*LMS Updates:* Regitration form validation changed: a "Retype password" must be entered and be equal to "Password". A email is verified with MX record and communication to SMTP server.
*Manual test instructions:*
Open http://127.0.0.1:8000/register and try to:
1. enter different "Password" and "Retype password" and see a validation message;
2. enter a email with invalid domain and see a validation message;
3. enter a not existing email with valid domain and see a validation message (this may not work for some domains);
The pull request includes a new dependency on dnspython.