Separate out personas & authentication for (re)use in other projects

[nogweii]

So I'm not sure exactly how to go about this, so I'm mostly spitballing:

• In my project, Fisheye, I'd like to support more authentication protocols, like WebID, which requires a FOAF profile. I would assume that it could just use Persona, but that feels a bit hackish and too tightly coupled. (I'd like to be able to include a switch and OpenID/masq is loaded if wanted, otherwise not.)
• I'd also like to look at various back-end authentication changes, such as using LDAP. In theory, it should be "as simple as" switching to Devise or OmniAuth.

This might need to be split up into separate issues if it's a larger change than I think it is.