Add GZIP filtering for text resources
NOTE: only compress text-based resources. Images and other compressed binary files do not benefit from GZIP.
Add a GZIP filter by default for *.css & *.js. The ehcache GzipFilter (http://ehcache.org) implementation works well and would not conflict with different versions of Servlet containers. See http://stackoverflow.com/questions/4755302 for more details.