Use correct spelling for authorisation event

Adyen is not american :)
Move notification processing step into the utility file

This will make it possible to reprocess a notification, when the code
to process it has been updated if there's a bug... Or other situation
that was correctable.
Add tool to reprocess nofifications if they were for some reason ignored
Send email on every Adyen payment

For now - to match what we have from Paypal. We may consider dropping
this later when we have more payments, but for now we want to keep track
of everything.
Remove unicode character in code
Correct list of available creditcards for Adyen
Clarify Paypal text, especially around requirements on accounts

This includes recommending using the Adyen payment processor for
creditcard payments, since we have lower fees there.
Render link for external viewing of invoices

We already supported viewing an invoice wihtout being logged in if you
had the secret, we just didn't show it on the actual page. Doing that is
useful for example when somebody wants to pay for their colleague.
Show the amount of transaction statuses

This is fetched in from the corresponding notification, as we don't
actualy bother keeping track of it on a per-status basis.
Fix typo!