Fix error handling

[mcmancini]

Check and fix how errors are handled. For example, the method run() in WofostSimulator contains a conditional statement allowing to deal with whether the simulator needs to run a single crop or a crop rotation. Currently, there is no error handling for running single crops; error handling in the crop rotation is poor (for example if there is an error, f"rotation '{crop_or_rotation}'") prints the entire rotation object rather than something meaningful.