Standardize definition of catalysts/ligands/complexes

[connorcoley]

"Most of these reactions involve metal catalysts and there’s no good way to represent them. Sometimes it’s a Pd catalyst with Buchwald ligand, its commercial and has a CAS number, sometimes it’s a customized ligand, with precatalyst and different activation approaches. I think the aim is not to find a perfect way to represent them, but just needs to be consistent across all the data. It might be helpful to provide a template for metal catalyst and ligand, and how they are set up for the reactions, instead of just letting the user run wild and draw their own structure."

(based on feedback from alpha tester)