Added catalysts into preconditions. Warning: multi-atom catalysts are
not working correctly due to not having atom-to-atom mapping numbers.
Proposed solution: once the generic reaction is created, count the
maximum possible number of atoms any instance of the reaction may ever
have, and enumerate catalyst atoms starting from max+1. Problem with
proposed solution: arbitrary alkyls can be arbitrarily long. Alternative
solution: enumerate catalyst atoms while ignoring r-groups, and then
change r-group enumeration to account for that.