Added new DynaBeanPropertyMapDecorator.

This is a new decorator class providing Map-like access to a DynaBean which
uses the correct generic type parameters <String, Object>. It will be used
internally by DynaBean implementations to provide a Map-view on their data.

git-svn-id: https://svn.apache.org/repos/asf/commons/proper/beanutils/branches/java5@1536077 13f79535-47bb-0310-9956-ffa450edef68