Create truly constrained non-deterministic dates

As with numbers in #2, dates should also be created according to an appropriate assumption about a proper default Equivalence Class.

The `RandomNumericSequenceGenerator` class could supply the [number of ticks](http://msdn.microsoft.com/en-us/library/z2xf7zzk.aspx) for creating [DateTime](http://msdn.microsoft.com/en-us/library/system.datetime.aspx) instances.