Let's help the user register :)

We should implement the following methods:

• registerUser() in UserService class
• validate() in PasswordValidator class

Method validate() should compare the password field with the repeatPassword field and check if their length is more or equal to 10. If not, throw exception PasswordValidationException with the message "Wrong passwords" (since it's our custom logic, let's create our own, CHECKED, exception because the user can put any password and our service shouldn't be broken. We should handle the not-valid case and return the understandable message).

Method registerUser() should call the method validate() and handle the exception. If everything is okay, save the user to the database (use method saveUser()), if not, print the message "Your passwords are incorrect. Try again.".