Implement unrestriction operation on PureStrategyProfile.

Provides an implementation of the operation Unrestrict() on
PureStrategyProfile.  This maps the given strategy profile on its
game, to the equivalent one on the unrestriction of that game.
Refactor gambit-simpdiv Nash solver to be derived from Nash solver class.

This refactors the implementation of gambit-simpdiv so it is expressed
as a subclass of the Nash solver class.

This is old and untidy code.  As such, this commit is largely about
making the public interface to the routine compatible with the Nash
solver framework.  The internals remain less than ideal.
PureStrategyProfile Unrestrict

Conflicts:
	src/libgambit/game.cc
	src/libgambit/game.h
All instances of StrategySupport refactored to StrategySupportProfile

No functional changes made on Strategy Support

Also for nfgsimpdiv.cc a few lines were changed to correctly compile