Add better heuristic to determine optimal request filter

[ridoo]

Currently, the hydro connector filters according to procedure parameter. This however is related to sample SOS instances serving just one observableProperty which resulted in an ExceedsSizeLimit exception during GetFeatureOfInterest.

Switching observableProperty filter and procedure filter would not solve the problem optimal as other SOS instances may be modeld the other way.

proposed solution:
Add kind of a heuristic that chooses that filter parameter which has less values. If still an ExceedsSizeLimit exception is returned, a combination of observableProperty and procedure filter should be used.

[ridoo]

To gain a quick solution for this problem we introduce a (temporary) separate connector which optimizes request filtering via observedProperty. However, the focused heuristic will integrate both cases later on.