password reset

[papousek]

For users who are registered via e-mail, we should provide resetting their password.

[slaweet]

We should also verify the email on registration by sending an activation link.

[papousek]

This feature is already present in Django, see:

• http://garmoncheg.blogspot.cz/2012/07/django-resetting-passwords-with.html
• https://docs.djangoproject.com/en/1.9/topics/auth/default/#django.contrib.auth.views.password_reset