Added QIIME2 custom reference database support. #1240

Job	Run time
Choose nextflow versions to test against depending on target branch	1s
nf-test (latest-everything, test, docker)	20m 12s
nf-test (latest-everything, test_single, docker)	5m 38s
nf-test (latest-everything, test_fasta, docker)	3m 25s
nf-test (latest-everything, test_failed, docker)	15m 54s
nf-test (latest-everything, test_multi, docker)	9m 6s
nf-test (latest-everything, test_reftaxcustom, docker)	6m 31s
nf-test (latest-everything, test_doubleprimers, docker)	11m 1s
nf-test (latest-everything, test_iontorrent, docker)	8m 13s
nf-test (latest-everything, test_novaseq, docker)	3m 50s
nf-test (latest-everything, test_pacbio_its, docker)	8m 40s
nf-test (latest-everything, test_sintax, docker)	18m 19s
nf-test (latest-everything, test_pplace, docker)	11m 30s
	2h 2m 20s

Provide feedback