Update docs, citations and usage with new taxonomic reference databases #1298

Job	Run time
Choose nextflow versions to test against depending on target branch	1s
nf-test (latest-everything, test, docker)	19m 50s
nf-test (latest-everything, test_single, docker)	4m 55s
nf-test (latest-everything, test_fasta, docker)	3m 12s
nf-test (latest-everything, test_failed, docker)	15m 7s
nf-test (latest-everything, test_multi, docker)	9m 28s
nf-test (latest-everything, test_reftaxcustom, docker)	7m 53s
nf-test (latest-everything, test_qiimecustom, docker)	7m 18s
nf-test (latest-everything, test_doubleprimers, docker)	9m 14s
nf-test (latest-everything, test_iontorrent, docker)	5m 34s
nf-test (latest-everything, test_novaseq, docker)	4m 18s
nf-test (latest-everything, test_pacbio_its, docker)	8m 58s
nf-test (latest-everything, test_sintax, docker)	17m 18s
nf-test (latest-everything, test_pplace, docker)	11m 56s
	2h 5m 2s

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