Added is_unit_simple compile-time traits.

I also generalized the Facade class by adding the constant DenumeratorBaseTypeValue = 1 which is the same for all Facade implementations.

Also, one major drawback occurs. I encountered various kinds of partial specialization ambiguities while adding various physical constants definition. I was able to get rid of the ambiguities by using enable_if boost technique with the is_unit_simle traits. But, I came to the conclusion that the compile-time unit template reduction method (with lots of explicit partial specialization) is not a viable way to handle reduction. I have to rework completely that part of the code.