BeanHelper now provides a shared default instance.

This instance can be used by an application if no special configuration is
needed. All references to BeanHelper's static methods (which occurred
exclusively in builder classes) were changed to use this default instance.

git-svn-id: https://svn.apache.org/repos/asf/commons/proper/configuration/trunk@1520795 13f79535-47bb-0310-9956-ffa450edef68