Monkeysphere improvements

• Adds GPG key publishing for HTTPS certs (snakeoil and Let's Encrypt).
• Adds detail view for each key with instructions for signing the key.
• Consistently use "OpenPGP" to describe keys and fingerprints.

Known Issues:

• There's no way to tell directly if the keys imported into Monkeysphere were from the snakeoil cert, or from a Let's Encrypt cert. So it's possible some keys could be displayed in the wrong table. One solution may be to keep some information about generated keys in the Django kvstore.
• The Monkeysphere browser add-on for Iceweasel doesn't seem to work (see https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=769441).