Improve OO encapsulation of StrategicSupport class

by John Benjamin for Gambit: Software Tools for Game Theory

This is a project to improve the general Gambit framework for implementing a Game Theory solution algorithm. An efficient game solving algorithm should never search for solutions over a support with one or more strictly dominated strategies. The Gambit framework captures this concept for any algorithm to build upon, but only indirectly. This project will improve upon the framework so that a C++ StrategicSupport object is available to algorithms as a complete representation of possible equilibra.