fix: mistake when given single row matrix
chg: moved listOfFacets to bbcone.cc where it belongs
chg: various new features

added features for tropical geometry (req by andreas):
- tropical variety of a polynomial
- common refinement of two polyhedral fans
- Polymake::vertexAdjacencyGraph
- Polymake::vertexEdgeGraph

also added various features for polytopes which were already available for cones, changed documentation accordingly