Define Use-Cases related to automated payment

[scaphilo]

Prepare answer to the following questions:

• What kind of use cases that require automated payment shall be supported by koalixcrm in future

[derek-adair]

1. I would like to include payment integration with installing a single submodule from this repo. Something like `koalix.payments'.

2. This should work out of the box with at least one of the following;

• stripe
• Brain Tree
• Paypal
• Authorize.net

3. Configuration via os.environ.get(). Each of these platforms has specific configuration. At first it would be easiest and fastest to pick one of the above and fully support it.

4. Optionally install each one of this in a further submodule... 'koalix.payments.stripe' for example

[derek-adair]

5.Integration with various transaction types;

• Subscription
• Refunds
• One off payments ... I'm sure therea re more i'm not thinking of.

6. MAYBE track payment types. It may be useful to have that referenced somewhere on an invoice or order form.

[derek-adair]

7. Invoice creation - (using the stripe vocabulary) Creating an invoice should optionally create a charge w/ <payment_gateway>. If a charge is created, create a form and expose it via {{SITE_NAME}}/payments//pay. Send a link to said page to the customer asking to pay.

[derek-adair]

8. NICE TO HAVE: Invoice expiration reminders/dates. Given an invoice expiration date, send out an alert to both partiers that something is about to be past due.