Polygon support for addressSearch

[oeninghe-dataport]

The addressSearch should (additionally) support working with polygons instead of points.

If a service is able to return a polygon, this should be preferred over points (or at least, it should be configurable).

Having the polygon allows for determining the adequate zoom level for the feature. The adequate zoom level should at least show the whole area of the polygon.

This issue is meant to be resolved when the following is implemented:

• addressSearch supports providers that return polygons.
• The nominatim addressSearch provider can be configured to use polygons.
• If polygons are used, the adequate zoom level is dynamically determined.