Potential improvement to Nextflow for Genomics

[vdauwera]

Suggested in a previous PR, saving here in case it's useful for the Genomics rewrite:

This is the equivalent splitCsv():

reads_ch = Channel.fromPath(params.reads_bam)
                .splitCsv()
                .map { bamPath -> file(bamPath[0]) }

I think it looks nicer

Originally posted by @adamrtalbot in #438 (comment)