Better handling of hazards for starting materials

[jdbocarsly]

We have the ability to specify hazard codes in the starting material GUI, but no validation or special handling at the moment. We should add a nice UI showing pictograms.

[ml-evs]

I'm thinking we should make another intermediate model for Substance that incorporates CAS, safety info, chemical formulae and other specializations, which would allow us to hide and share this logic across models. Sample and starting material can then inherit from this, but presumably cell and other devices would not.