Add test-cases in order to evaluate AOI algorithm

[sfkeller]

Add additional test-cases in order to evaluate the AOI algorithm and it's parameters. This is a prerequisite e.g. for #8.

Test cases are polygons of rural areas manually drawn by someone with local knowledge. Before adding these AOI pls. read the definition what AOI are in the README of the repo homepage: https://github.com/geometalab/aoi-osm/ .

Adding AOI test-cases can be done in several ways, like simply adding a comment below.

The preferred form is threefold: note 1. the name of the location and 2. the center coordinates (e.g. "Halle (BE); 50.73601,4.23786") and 3. refer either to a GeoJSON file (e.g. as Github gist) or publish a uMap (like http://umap.openstreetmap.fr/nl/map/manual-aoi-halle_239532 ).

AOI test cases are collected here: https://github.com/geometalab/aoi-osm/tree/master/test-cases .