Replace hardcoded url in password reset notification email with site name (from django_site table)

registration/password_reset_email.html

@@ -3,7 +3,7 @@
 
 {% trans "Please go to the following page and choose a new password:" %}
 {% block reset_link %}
-https://6002x.mitx.mit.edu{% url 'django.contrib.auth.views.password_reset_confirm' uidb36=uid token=token %}
+{{ protocol }}://{{ site_name }}{% url 'django.contrib.auth.views.password_reset_confirm' uidb36=uid token=token %}
 {% endblock %}
 {% trans "Your username, in case you've forgotten:" %} {{ user.username }}