Email validation

[jensneuhaus]

☝️What is it? Why do we need it?

This issue works together with #30

We need a logic to validate email to make sure, the emails we sent arrive at the correct inbox.

In DARE we had the logic that the user account logic (is_active) is tight together with the email validation but actually these are two different things.

1. We mark a User as active (e.g. after correct Email verification)
2. We know, that the Email is verified

It could be possible to turn a User to inactive and still know, his email is verified. Or to set the User to active with an unverified email.

💭 Implementation details

📋 Todos

• [ ] Check on https://django-rest-auth.readthedocs.io/en/latest/api_endpoints.html#registration logics on Email verification and make sure it works nicely with the correct allauth approach to save different email addresses : https://github.com/pennersr/django-allauth/blob/master/allauth/account/models.py#L18
• [ ] Make sure Sign up / Email verification work together nice enough