[7.1] Move Bean Validation documentation to a top-level chapter

Bean Validation documentation (https://access.redhat.com/documentation/en/red-hat-jboss-enterprise-application-platform/7.0/development-guide/chapter-13-hibernate#bean_validation) is currently part of the Hibernate chapter of the development guide. However, Bean Validation is not really specific to Hibernate and it can be used together with other Java EE frameworks as well. I suggest to promote it to a separate chapter independent of Hibernate.