CDK-496: Incorporated review feedback and made Constraints type aware.

Being able to pass the type when loading a dataset brought to light
potentially dangerous type conversion issues with constraints. Since
constraings already had to normalize the constraints that were coming
from View URIs, I updated constraints to be type-aware and to convert
all constraining values in a consistent mannger. This should make it
much easier to create constraints even if you switch between Generic,
Specific or Reflect data models.