Filter the presence of seeds in the scope by removing seeds absent from the network

[cfrioux]

Context

When running mene scope, one can provide a set of seeds that contain any metabolite, including some that do not belong to the considered metabolic network.

Current behaviour

As the definition of the scope includes the seeds, these non-relevant compounds will be outputted as belonging to the scope.

Solution?

We could exclude these from the scope, and why not create a predicate to distinguish them as it might be a good debugging tool to catch these compounds.

While we are making modifications, we could also create the predicate "non_produced_seeds" as a complement to "produced_seeds" to help filter seeds after computation.

@ArnaudBelcour what do you think? Will it have any unwanted consequence on m2m?