Re #379: Fix validation of requirements to check for unit * Rename public accessor for unit types to ConstraintTypes so that "no more than" requirements don't work with "required types" * Remove class level version of ConstraintTypes to fall back to abstract class version * Make sure we cascade allowedObject up through RequiresNoMoreThanNOfUnitTypeRequirement * Rebuild UnitRequiresNoMoreThanNOfUnitTypeRequirement "IsApplicable" so that we don't get applicable for unrelated types, even if the requirement is currently in a failure state