MOF14 — Can MOF Class contain a Constant?

The MOF 1.3 Specification shows in table 3-4 that a Class can contain a
Constant. But constraint [C-15] ClassContainmentRules does not allow a
Class to contain a Constant. The table and the constraint need to say the
same thing. Since MOF's Model.ModelElement contains Constants, it is clear
that the table is correct.

Recommendation: add Constant to ClassContainmentRules.

Change constraint [C-15] as recommended