Defines the current set of default values used for data.
This is a static class because we need to ensure that the defaults and constraints used by the RandomGenerator to create anonymous test data are the same defaults and constraints used by the DbHelper to insert those values into the database. The main case for this is when a date value is supposed to be null, the min sql value is used (since it cannot be null in memory). When inserting the data..if the value is the min value, a DBNull is actually inserted. The comparison against min value to determine if a DBNull should be inserted is the purpose for this class and the DefaultConstraints class.