PAXWEB-758 cache the classloader information to improve the effeciency, especially for web service application

When using pax-web for web service application, the classloader is not so efficiency, e.g. for SOAP, it need to load the xml factory everytime, and current ResourceDelegatingBundleClassLoader will trigger a loop for look up, which consume much cpu.

So just implement a Most Recently Used (MRU) cache to improve the performance.