Provide public API for constraint match reporting

Up to know I found 2 inquiries about providing API to access constraint occurrences or related data (PLANNER-96; PLANNER-189).

Both suggested a particular solution that did not fit very well in the current architecture of optaplanner.

I will try to state a problem in a solution agnostic way:

Currently it is easy™ to get e.g. a score of the solution. Alas, it is not enough to give sufficient information to the user about WHY the solution is the way it is. I mean, saying "the solution has score of 0 hard and -12334 soft" is not sufficient to explain human planner why the solution is the way it is. Furthermore, a numeric score does NOT tell where in solution there are deviations from the optimum.

So I move that we need some PUBLIC interface for the easy™ retrieval of detailed constraint match information in one form or in another.

This public interface should NOT require complex initialization and should be accessible over the popular (or new) classes of the public interface ideally - over the solver or solution.