Add subscription flow to example project

[Viincenttt]

• Add the option to set the sequenceType, customerId and mandateId when creating a payment
• Add the option to pay a recurring payment using the ChangePaymentState link
• Add the mandateId and description columns to the subscription overview
• Add the option to set a description when creating a new subscription
• Fix issue where you couldn't create a mandate for a customer because the ConsumerBic property was not set