Added configuration option to only allow OpenID logins.

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.

config.php.sample

@@ -38,6 +38,8 @@ $config['site']['path'] = 'laconica';
 // $config['site']['closed'] = true;
 // Only allow registration for people invited by another user
 // $config['site']['inviteonly'] = true;
+// Only allow registrations and logins through OpenID
+// $config['site']['openidonly'] = true;
 // Make the site invisible to  non-logged-in users
 // $config['site']['private'] = true;