GaudiConfig2: apply OrderedSetSemantics to std::[unordered_]set

Frank Winklmeierrequested to merge
fwinkl/Gaudi:setsemantics into master

Apply the OrderedSetSemantics by default to std::unordered_set and set::set. This fixes e.g. problems when merging the ExtraInputs/Outputs properties of algorithms.

Replaces !1295 (closed).

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