Invitations can now be configured through admin panel settings. By
default, invitations are enabled. Invitation system is also available if
registrations are disabled. To completely remove the ability of new
users to sign up, disable both registration and invitations.
Fixes#330
* Removed old registration configuration option from config file
* Changed database registration option to allow registrations by default
* Changed admin settings template for new DB option
* Changed registration controllers for new DB option
Fixes an issue with registrations not working if settings table is
empty.
This will allow any admin to enable or disable a pool maintenance mode.
Regular users that are still logged in will not be kicked out (yet). New
users that are trying to login and are not admins will be denied access.
Also added registration option to Admin Settings via WebUI. You can now
disable new accounts via web option or configuration setting.
Fixes#259 but also adds an additional feature.
* Adding new configuration variable, see `global.inc.dist.php`
* If you are not able to register anymore check the config var is
* set
Requested in and fixes#150
