add/remove_species are no longer supported by Space/World
renamed Model::add_species -> add_species_attribute
implemented apply_species_attributes
apply attributes to a species before creating a new molecule
wrapped apply_species_attributes and get_species in NetworkModel
updated a sample for reaction_reader
renamed get_species -> create_species
for a sample, species_attributes seems better than species_attributes_with_keys
updated a sample in spatiocyte_python