euk contamination hmm shouldn't be hardcoded

[wwood]

Hmmer.py:            nhmmer_cmd = "nhmmer --cpu %s %s --tblout %s /srv/db/graftm/0.1/HMM/Euk.hmm " % (threads, eval, out_table)
Hmmer.py:            cmd = "nhmmer --cpu %s %s --tblout %s /srv/db/graftm/0.1/HMM/Euk.hmm %s 2>&1 > /dev/null " % (threads, eval, out_table, reads)

Maybe we need some kind of 'GRAFTM_DB' environment variable or something, where all the gpkgs live and then the user can specify them by name rather than path, and euk 18S can just be one of those. Just to make things easier. It should also be possible to specify the euk HMM directly on the cmdline though.