If $config['openid']['enabled'] is set to false, OpenID is removed from
the navigation and direct accesses to OpenID login pages redirect to the
login page.
If OpenID is enabled, $config['site']['openidonly'] is ignored, i.e.
OpenID is required to go OpenID-only.
If $config['site']['openidonly'] is set to true:
* the Login/Register pages will be removed from the navigation;
* directly accesses to the Login/Register pages will redirect to the
OpenID login page;
* most links to the Login/Register pages will link to the OpenID login
page instead.
The user will still need to set a password to access the API and RSS
feeds.
