Support numeric ranges for Concepts using ConceptNumeric

Concepts of numeric type can have pre-defined valid ranges for them. These are managed through the ConceptNumeric object. We need to be able to CRUD these ranges using REST calls. It would be simpler if these ranges can be shown as part of the concept representation if they are numeric type and not otherwise.
Some discussion here: https://groups.google.com/a/openmrs.org/d/msg/dev/H34aTqINZWo/uohM7drxopUJ

bwolfe: Can we just add the properties to the Concept resource to show up only when its a numeric concept?

djazayeri: So, one approach would be to write a SubclassHandler for ConceptNumeric and register it with ConceptResource.
But Concept is a bit different from Order in that we expect and want to support modules defining new types of Orders, but we do not support modules defining new kinds of concepts. So, since the set of all available concept types is known ahead of time, we could take an alternative approach, and make the Concept resource transparently behave like a ConceptNumeric (i.e. show more properties) if it is one. This would work for GET. Someone should think through how that would work for POST...