Better structure to hold pesticide parameters

The pesticide parameters are saves in mod and spec. This makes sense in some way because for example the half-life of a pesticide is for all species the same but not the LC50. Maybe one option is to make a big pesticide struct in mod, where every pesticide gets their own object with PesticideID (the injection struct already has that) and a sub-struct with the effects on the single species indexed by SpeciesID.