graphics/py-contextily: Add py-contextily 1.6.0

contextily is a small Python 3 package to retrieve tile maps from the internet.
It can add those tiles as basemap to matplotlib figures or write tile maps to
disk into geospatial raster files. Bounding boxes can be passed in both WGS84
(EPSG:4326) and Spheric Mercator (EPSG:3857). See the notebook
contextily_guide.ipynb for usage.

The current tile providers that are available in contextily are the providers
defined in the xyzservices package. This includes some popular tile maps, such
as:
- The standard OpenStreetMap map tiles
- Toner, Terrain and Watercolor map tiles by Stamen Design