Make result deduplication configurable

[lonvia]

Photon currently has a simple mechanism to deduplicate results when they likely refer to the same real-world object. The algorithm for that is hard-coded and restricted to simple street deduplication. It would be nice to make this configurable per instance. For one thing, the exact definition when to results differ may vary (e.g. do to street parts need the same postcode?). For another, it would be nice to extend the mechanism to other objects, for example to deduplicate bus stops.