Implement database-based user management

php/controller/register-controller.php

@@ -1,6 +1,6 @@
 <?php
 
-require_once "php/model/LocalUserManager.php";
+require_once "php/model/UserManager.php";
 require_once "php/validator/user-validator.php";
 
 $error = null;
@@ -22,7 +22,7 @@ if ($_SERVER["REQUEST_METHOD"] === "POST") {
         $error = "Das Passwort muss 8 bis 72 Zeichen lang sein.";
     } else {
         try {
-            $dao = new LocalUserManager();
+            $dao = UserManager::getInstance();
 
             $password = password_hash($plainPassword, PASSWORD_DEFAULT);