Influence terms and reaction terms and built and destructed by
influence/2 and reaction/2.

add_reaction/* is no longer a part of the public API: use reaction/2 and
add_item/1 instead.

influence_graph and draw_influences now infer again the inference graph.

reaction_graph/draw_reactions and
influence_hypergraph/draw_influence_hypergraph draw the (hyper)graph of the
reactions and influences respectively.