fully seperating chemical_entities_ap and chemical_reactions_ap as distinct schemas

[HendrikBorgelt]

currently chemical_entities_ap requires has_molar_equivalent as a slot of ChemicalSubstance. has has_molar_equivalent however is only defined in chemical_reaction_ap. As such, new schemas which only want to import the chemical_entity_ap description will currently fail due to missing the slot. Here this has now larger consequences, since chem_dcat_ap imports material_entites, chemical_entites and chemical_reaction, such that no aspect is missing. However, in a separate project, where I don't want to include the chemical reaction description, this causes some issues.

[StroemPhi]

I defined it in chemical_reaction_ap.yaml because it only makes sense in the context of a reaction, but you are absolutely right. I guess the easiest way to fix it would be to copy the slot definition from there to chemical_antities_ap.yaml.

[StroemPhi]

rereading #59, I'd rather opt for the fix I propose there, which means to just drop these two slots from the slot list of ChemicalSubstance.