Localized by classloader

**This improvement enables struts to be used as JBoss AS 7/WildFly 8/JBoss EAP 6 module.**

_**Issue:**_
having two or more applications using the same "struts-module" (meant as JBoss AS 7 module),
each application with its own resource bundle, the first one which initialized the LocalizedTextUtil "wins" over the second and next application's resource bundles. Furthermore, to avoid overwriting bundles, now each bundle is indexed into the bundlesMap by its key (resourceBundleName) and prefixed by ClassLoader hash code.

https://issues.apache.org/jira/browse/WW-4379
But do we need synchronization at all if we operate on `ConcurrentMap`?