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 think even post-init file we'll need a way to encode this sort of information, whether it's custom properties in the CKAN record or something else.  I agree about extending out our GetCapabilities support to look for tile information.