Allow for mouse host in host read removal

[rroutsong]

Allow for mouse read removal in host read remove

This will require accepting a command line parameter specifying mouse or human host, and switching the -x flag in the rule metawrap_read_qc & rna_read_qc

[skchronicles]

Once @GaryZhangYue's branch is merged, let's add an option to the pipeline called --host-remove {human, mouse}, where the default is set to human. We can set it up to point to the bowtie2 indices for DNA and the STAR indices for human and mouse.