tests: test cases to new AccountController

The AccountController is now using BindingResult for returning errors to
the registration form, so the test cases needed to be changed.
refactoring: removed Result and RegistrationError

We now use Spring to evaluate the input data, so there is no more need for
these classes in the example code.
refactoring: renamed example.springmvc.data to example.springmvc.model
tests: added test case for user service