Revising the bpugraph concept

We need a public but very limited ANode and BNode class
It can be used with ItemSetTraits and with some special maps

By example:
DescriptorMap<Graph, ANode>
InvertableMap<Graph, ANode, string>
IterableBoolMap<Graph, ANode>
IterableIntMap<Graph, ANode>
IterableValueMap<Graph, ANode, string>

/* Define to 1 if you have CPLEX. */

#undef HAVE_CPLEX

/* Define to 1 if you have GLPK. */

#undef HAVE_GLPK