Add hibernateEmail validator

[philippd]

Add new validator for email addresses using the regex used by Hibernate Email validator: http://docs.jboss.org/hibernate/validator/5.1/api/org/hibernate/validator/constraints/Email.html

This validator will be used for @Email annotations when the valdr-bean-validation plugin is used for the back-end.

see #24

[philippd]

Basic validation implemented with 462653e

Still have to figure out where the hibernate validator considers the regex and flags parameters.

[philippd]

The Hibernate implementation of @Email does not support regex (and therefore flags), so we'll skip this for now...