Add hisat support

[rekado]

This is a variant of https://github.com/BIMSBbioinfo/pigx_rnaseq/pull/93

Instead of replacing STAR with hisat2, this PR adds rules for Hisat2 use.

TODO:

• read MAPPER value from config file
• remove Hisat2-specific file names from 'final-report' target
• test this!