[CF-14] improve servlet filter perf

TransformerUtils has this comment that "it is not thread safe and a single instance of this is meant to be used for one pair of servlet request and response." We looked into it and didnt want to take our chances by having one instance across requests. So I yanked out xslt transformation out of it and put it in a separate class. An instance of XSLTTransformerUtils can be used across requests.