support for wms-c / geowebcache

Some syntax fixes so that GeoWebCache will work with NM in direct integration mode and as WMS-C.  This partially addresses #473.

WMTS and TMS require additional ViewModels or extensions to the WebMapService view models.
I believe servers that support tiling but that don't support the specific tiling scheme we've requested are supposed to fail when given `tiled=true`, so this may be dangerous.  In my experience GeoServer doesn't do this, but others might.  Better to specify this parameter in the init file when we need it than to always enable it.