SpringAtom-#133

fixes #133

General changes:
- added EventListener.java annotation for listeners in application to be picked up by classpath scanning
- added UserRegistrationException.java which is thrown in case of error during registration
- Extend NewUserWizardStep3.java to catch any exception thrown during registration:
 - exception can be either UserRegistrationException.java or the one related to the constrains validation

- SUserAuthoritiesSavingListener.java is working after user was persisted and handles persisting of its authorities

Validation steps:
- added UserCombinedValidator.java for ValidUser.java validating annotation