Apply for membership

• Change building of the request for the use case - don't use individual setters for payment data (amount, interval, payment type, iban, etc). Instead, build a PaymentCreationRequest and set it.
• In preparation of the coming bank data payments, set the transfer code prefix to "XM" (see T312087: Change backend code to meet bank transfer requirements)
• Remove all branching that checks the payment type. .
• ~~ Remove URL generators from the fundraising application repo.~~
• Fix the converter that takes a donation and turns it into values for the membership form.

Validate Fee
Use new payment class

• Cancel Membership**

Fix unit tests. With the adapted fixtures this should be straightforward

Notes

• There is a CLI tool to test confirmation mail output.