Fix signalP typo in group_info and refactor method

The original reported bug was that a pangenome or panproteome with signalP annotations always crashes at the retrieval of the signalP information with pantools group_info with a NullPointerException. This was caused by a copying typo in this specific method. However, when debugging, I also found that pantools group_info doesn't work on panproteomes. For this, I split the main information retrieval from mRNA nodes in two methods: one for pangenomes and one for panproteomes.