Merge preprocessed datasets from the same library before mapping to mag catalogue

[anttonalberdi]

We have now started to resequence some libraries to increase sequencing depth. We therefore need to implement a way to merge datasets that derive from the same library before mapping the reads against the MAG catalogue. The "IN Code (from EHI_number)" column at the PR_Preprocessing table in the EHI MAG database contains the library information. I therefore suggest that whenever there are PR samples with identical IN code, these are first merged. Ideally, the combined sample should be named EHI01149_EHI01150, but I am not sure whether that will be feasible.