LAST alignment statistics for MultiQC

[charles-plessy]

This PR adds a multiqc output channel to the last/train, last/lastal and last/split modules. The new channel provides statistics in TSV format.

For last/lastal the MultiQC file contains some of the alignment parameters determined by this module. Their value is quickly retrieved by parsing a text file.

For last/lastal and last/split, the MultiQC file contains the total alignment length and percent similarity computed on the fly while the alignment is being performed.

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