Derive human-friendly openid realm from publicUrl
Disable openid favicon. Broken as of ee33e26.

When sending a realm like https://*.persona.org, Google looks for the favicon at
https://www.persona.org/favicon.ico.

We currently 404 there, so this commit temporarily disables the icon option.
Merge pull request #96 from mozilla/realm

Use a human-friendly OpenID Realm