[GEOS-3847/GEOS-5359] Integration with GWC Pluggable URL Mangling

Takes advantage of the addition of pluggable URL mangling to GWC with a mangler that delegates to GeoServer's own mangler.  Resolves tickets GEOS-3847 and GEOS-5359.  Applies to WMS, WMTS, TMS, and REST layers.xml

Requires patch to add functionality to GWC, pull request pending: https://github.com/GeoWebCache/geowebcache/pull/145