Improve Monkeysphere module

Created by: SunilMohanAdapa

Basic module for host SSH key publishing is now available. The following improvements can be done:

• Implement similar GPG key publishing for HTTPS certificates generated by Let's Encrypt and snakeoil certficates also.
• Implement revoking keys.
• Add detail view for each key, with instructions on how to sign it.
• Add SSH client authentication. This will require linking box usernames to email addresses.
• Be consistent with use of terms like PGP, OpenPGP, GPG.