Add module to check and preprocess samplesheet

[grst]

At the very beginning of the pipeline, we need to verify that the samplesheet makes sense, and
sanitize it.

For instance, the samplesheet used by nf-core/rnaseq can contain multiple rows for the same sample (in case multiple fastq files need to be merged).

Input: samplesheet as provided by user
Output: cleaned samplesheet with one row per sample.

[grst]

Section in the old code:
https://github.com/icbi-lab/deseq2icbi/blob/28e54a75598d39b70090376daa0e9ddefee25363/runDESeq2_ICBI.R#L159-L183