Ability to use a custom DecoratorFactory

Currently, the DecoratorFactory is a utility class that has 2 static methods. It would be nice if it was a user specifiable implementation of a simple interface with those two methods. (You could store it in the servlet context to avoid having to reinstanciating it everytime).

Doing this would allow to have (for instance) a DecoratorFactory that retrieves decorators from an ioc container, allowing them to enjoy the power of dependency injection. (One could also have a caching implementation, which would for instance keep an instance of each decorator per thread (using a ThreadLocal), avoiding many reinstanciations of the decorator)