switch to an unordered map for LabeledValueSet

Currently a private map keyed by unsigned int is used and no iterating method is defined so it is safe and perhaps faster to use an unordered map i.e. a hash table instead a balanced binary search tree.

LabeledValueSet is used in state models which are themselves used to handle HTTP and JSON input.

Note an alternative is to get rid of the LabeledValueSet and to use directly an unordered map in StateSet as I am not happy with the StateSet::getState() method performance which is called in the runModel loop.

Or moved for LabeledValueSet to a template taking a shared pointer to LabeledValue derived object type parameter and of course LabelValuePtr for default.