Fix keys with utf 8

Closes #1

See merge request !1

If wkd-srv runs with LANG=C (which is what happens in our images),
ruby will default to US-ASCII as the default encoding.

OpenPGP Key uids should be UTF-8 strings, thus let's switch to
UTF-8 as the default encoding.

Additionally, there are keys in the wild with broken character
encoding. Thus let's be more on the safe side and enforce UTF-8
strings.

See:

  * https://0xacab.org/schleuder/schleuder/-/issues/276
  * https://0xacab.org/schleuder/schleuder/-/merge_requests/325
  * https://0xacab.org/schleuder/schleuder/-/merge_requests/301

For more background on the details from another project.

Keys imported were fetched from the SKS network.

OCI image specification relies on GOARCH which defines amd64 for linux.

* https://github.com/opencontainers/image-spec/blob/v1.0.1/image-index.md
* https://golang.org/doc/install/source#environment

There is no need to use more complicated paths, and it makes life easier
for admins.

Only the error messages were JSON-encoded, which is unnecessary.
Even /status.json didn't responst with JSON-encoded content. That URL
has been changed to /status

The complex possibilities were not used.

This allows us to simplify the code in the route-blocks. In development
mode exceptions are not caught by the error() handler.