Add karstic areas

[Vayel]

Add a riskLevel property in the geoJSON for each point:

• 3 if sswi < -1.4 and in karstic area
• 2 if sswi < -1.4 and not in karstic area : https://stackoverflow.com/questions/20776205/point-in-polygon-with-geojson-in-python
• 1 if sswi < -0.7
• 0 otherwise