Include donation token in email receipt

[LeafHacker]

Since we set receipt_email on the payment_intent, Stripe will email a receipt to users on payment success.

Unfortunately our token isn't generated yet when this happens, but fortunately we can work around this by not setting the recepit_email field until after we've generated the token.

• Create payment
  • Store email in metadata
  • Do not set receipt_email yet!!
  • Consider setting statement_descriptor and statement_descriptor_suffix?
• Payment success
  • Update payment description with token
  • Set receipt_email using value stored earlier in metadata
  • Consider setting token in metadata too?