Start constructing linear pathways

modelpruner/__init__.py

modelpruner/core/model_pruner.py

modelpruner/core/protected_parts.py

modelpruner/graph/__init__.py

modelpruner/graph/linear_pathway.py

modelpruner/graph/linear_pathways.py

modelpruner/graph/metabolite_node.py

modelpruner/graph/network_graph.py

modelpruner/graph/pathway_segment.py

modelpruner/graph/reaction_edge.py

modelpruner/models/fba_model.py