add imagery by South Tyrol's provicial administration

* WMTS_OF2011_APB-PAB - aerial imagery from 2011, approx. 50cm
  resolution (not as good as bing, but much less distorted in the
  mountains)
* WMTS_TOPOMAP_APB-PAB - a detailed topographical map with contour
  lines, hiking paths, buildings, landuse, etc.

There is an explicit [permission](http://sdi.provincia.bz.it/geoserver/ows?service=wms&version=1.3.0&request=GetCapabilities) for the *„production of Open Data derived products”*. More on the OSM-[wiki](https://wiki.openstreetmap.org/wiki/AltoAdige_-_Südtirol#Provincia_Autonoma_di_Bolzano_-_Autonome_Provinz_Bozen).