Use public key fingerprints on personal profile documents

[cdchapman]

It would be good to list personal identifiers (specific to Pentandra) on the personal profile documents. Of course WebID, but also PGP keys for company email addresses (if applicable).

• Create fingerprints from the x509 certificate public RSA key within the certificate (WebID, either dynamically or as an attribute in var/company.yaml. Fingerprinting the RSA key because it's something that others could verify using only the modulus and exponent.
• Generate QR Codes from the fingerprint of PGP keys and display on the profile document. Use the openpgp4fpr URL scheme.