Improve user signup flow

[adewes]

The user signup flow is not very friendly, we should improve that.

[bkastl]

Random thoughts:

Usually it is either searching for appointsments inside a radius or using the access code to get access to a restricted location.

As the signup flow is heavily based on the si.de signup flow we should streamline that.

So the wizard style of the current signup has some unnecessary steps. I think it can be done with two simple steps:

1. your settings
2. backup code

When we integrate a sign up via mail etc. a verification by link / hash in link should be enough. I think there should be no additional user input necessary.

The settings selection will grow as there are different vaccination types right.

But let's talk about that together.