Encoding of adjacency directionality through use of `start` and `end` leads to complex queries

[mbaudis]

The encoding of adjacency directionality through use of start and end named parameters makes queries complex. It requires that one knows the direction of the fusion partners or creates some complex $or requests.

From the point of querying it would be cleaner to have directionality agnostic base parameters and then an optional parameter for direction (which - for queries - won't be used much in practice).

(I'm personally not sure if I find the indication of a location solely through an end parameter really elegant or rather odd... )