CAS-1207 Make cglib a direct dependency of cas-server-webapp.

Both cas-server-webapp and cas-server-integration-restlet depend on cglib; the former via transitive dependency on spring-json and the latter directly. Placing the dependency directly in the webapp artifact and removing it from the other locations cleans up the dependency graph when both webapp and restlet are used together. It's safe to remove the dependency from restlet since there is no use case for using it without webapp.
CAS-1207 Add maven enforcer rule to prevent banned cglib artifacts.
CAS-1251: Move the JsonExceptionView resolver to the management webapp

Addressed issues raised by Scott. Fixed the import location, used a direct "return null" instead of a stale variable and removed the message key constant.
Merge branch 'master' into CAS-1251

Conflicts:
	cas-server-webapp/pom.xml