Create ChangeUserEmailAddressController

[sloschert]

This controller is intended to be used in the change_email_address route in arbeitszeit_flask/user/routes.py. It has two methods. One, extract_email_addresses_from_token is used in the GET and the POST method of the route, the second method, create_use_case_request, is used in the POST method and creates the UseCaseRequest object of the ChangeUserEmailAddressUseCase.

Contributes to #728.

Plan-ID: 371825c0-3112-47cd-9cb0-fea799fad3ee (2x)

[sloschert]

Hey, regarding your comments:

• I will reduce the timeout to 15 minutes then.
• We have the function is_possibly_an_email_address in arbeitszeit/email.py and we make use of it for checking the well-formedness of the email-address in the use case ChangeUserEmailAddressUseCase. So the controller in this PR creates the request object for the use case where the email is then checked for well-formedness.
• We have no logic to handle the mentioned emails aliases for now. I have no strong opinion about it. let me know if you think that we should handle it now.
• We agreed more or less to keep the unit of work as small as possible, but I can make it a bit larger to make the bigger picture more visible. Or push PR drafts with upcoming PRs, that should help as well.

[sloschert]

@seppeljordan I register 2x consumption