nixpkgs/morph version handling improvements

this means we don't have to download it every time

Maybe I should be wasting my time learning about Hydra instead ...

Remove old Tahoe-LAFS incident reports

This gives us a good opportunity to mention the privacy policy, too.

Update PaymentServer to a version with improvements to concurrency relating to
SQLite3 usage.

This seems to improve the situation though does not completely resolve it.

At least, I suppose it was incorrect.  It won't build anywhere it has not
already built.  I don't know how it built where it already built.

Update PaymentServer and ZKAPAuthorizer and leak fewer secrets

Update PaymentServer and improve secret handling

Move morph configuration around so it is better placed

Also put library code in a library directory

Deploy a PaymentServer with CORS

The new version of PaymentServer has incompatible changes that require this.

Added system tests for Tahoe-LAFS link and unlink functionality

Tweaks for re-deployment of storage005

Deploy PaymentServer with Stripe API key