Co-authored-by: Shae <shae@scannedinavian.com>

* It's a poor way to represent application errors
* It's only intended for interpreting failed pattern matches
* I don't know how to consume it from an Obelisk frontend

* Instead of failed pattern matches, at least use MonadFail (which we already
  asked for)
* Use immutable lookupServer when downloading a CHK!

Generated cabal project local

See merge request !1