This changes how runtime for rules is specified. Before it was a parameter, now it's a resource. This has the advantage of that it works with the Slurm Snakemake profile, and that it can be used when calculating resources for a group job. Note that resources in Snakemake have to be integers, so the function
utils.to_min is used to convert from time strings to number of minutes. This should not be visible to the user, as he/she typically only sets runtime via the config object.