Upgrade to hibernate-validator 5.1.1

Remove "javax.validation:validation-api:1.1.0.Final" dependency because it comes transitively from hibernate-validator; there's no need for the redundancy.
Add "provided" scope dependency on "javax.el:javax.el-api:2.2.4" Hibernate-validator has long required this dependency but didn't enforce it as strictly until HV-793.
This dependency has to be scoped "provided" because all modern servlet containers and application servers include EL support.
If it's scoped compile, it will conflict with what the container provides and cause classloading problems.
Java EE 6 requires that EL 2.2 be provided. In addition to all Java EE 6 application servers, Tomcat 7 and Jetty 7 also include it.
Merge pull request #11 from candrews/patch-5

Upgrade to hibernate-validator 5.1.1