true_coverage module in innuca recipe

[cimendes]

Currently, the true_coverage module requires a species to be passed on as an argument, but a scheme is not available for every species. When this happens, the pipeline breaks with an error. This makes the innuca recipe unusable for other organisms. I suggest that when a species is set as Null, for this component to be bypassed. Otherwise, when the species is not included, a sys.exit is launched with an error code that then we can pass on to the nextflow component for it to be ignored. The last solution is more clean, in my opinion, but requires a PR in rematch's code.