Plugin hooks: authentication

[Alanaktion]

Plugins should be able to provide alternatives to the default Phproject authentication. I'm not sure how this should work yet, but it would make things like LDAP and OpenID authentication easily addable via plugin (which I'd like to keep out of the main project if possible, since they're likely not useful to many users).

[Alanaktion]

OpenID and similar methods can use a setup like phproject-plugins/googleauth, where a new route is added to send a token to, but this won't work for LDAP and other methods that require intercepting the core login credential verification.