plug in the url manglers with gwc's hook

GWC now has a hook for altering the urls that it generates. This plugs
into that hook, and delegates to the geoserver response utils chain,
which calls all the geoserver pluggable extensions.
added WMS and WMTS support for URL mangling
Fix for URL mangling base paths, and adding WMS and WMTS mangling
Merge branch 'master' into gwc-url-mangling-master
Merge branch 'master' into gwc-url-mangling-master
Merge pull request #53 from smithkm/gwc-url-mangling-master

[GEOS-3847/GEOS-5359] Integration with GWC Pluggable URL Mangling
Merge branch 'master' of git://github.com/geoserver/geoserver