ENH: Add reader for MZMV 2015

[bifbof]

Implementation of a reader of the "Mikrozensus Mobilität und Verkehr 2015" around 95% finished. It is not the cleanest implementation as the data needs a lot of massaging until we get it into the right shape, so it could be that there are some bugs that I overlooked so far. One point we should discuss is how we should handle triplegs without geometries (if we are lucky that are below 25% of all triplegs), should we drop them or keep them. So far our model says that triplegs without geometries are not valid.