[WIP] Mapproxy service extension

The aim of this PR is to provide WMTS tiles for other _projection_ than the used by map.geo.admin.ch using _MapProxy. The ultimate goal would be to use the same RESTful patten for _TileMatrixSet_ like ETRS89, WG89, LV95 and the ubiquitous spherical mercator.

_http://wmts.geo.admin.ch/1.0.0/ch.swisstopo.pixelkarte-farbe/default/{Time}/{TileMatrixSet}/16/1/5.jpeg_

The config file for _MapProxy, `mapproxy.yaml` is generated by a script reading the layers list from the BOD.

The 

* Using a WMTS source is no issue for MapProxy, but we have to define a new _layer_ for each _projection_, for instance `pixelkarte`is the original name, `pixelkarte.mercator` would be the name for the repojected layer in mercator, which is redonand.
* It is now not possible to forward

[to be continued]