Added non registered statistic

buisnesslogic/src/main/java/com/plannaplan/services/UserService.java

@@ -186,4 +186,11 @@ public class UserService {
         return response;
     }
 
+    /**
+     * @return ammount of how many users haven't created an assignment yet
+     */
+    public Integer getAmmountOfUsersWithNoAssignedGroups() {
+        return this.getAllStudents().size() - this.getAmmountOfUsersWithAssignedGroups();
+    }
+
 }