WIP: Try adding guest user library

[partizipation]

we decided to fork django-guest-user and add email and password for the guest authentication. See here

Couldn't get around the circular reference, tried a bunch of things. Code has a bunch of commented out attempts so it's a little messy but maybe this PR helps review.

Tried:

• all possible order of guest stuff, auth, and apps.users in INSTALLED_APPS
• importing in different ways from within users/models.py
• registering in users/apps.py in a couple different ways

[m4ra]

@partizipation @goapunk to enable the guest user from the registration form, I would add the maybe_make_guest_user in the a+ DefaultSingUpForm.save().
In that way we don't need a middleware. and the guest user will behave as a regular one. In the Account Settings we will need a check in the request.user if they have a user.geust relation then we should add the conversion form component instead of regular profile. Or something down this line.

[m4ra]

@partizipation the signup template to add the login as guest button is here. But I think the registration form is in a separate story.