Get SILVA reference files

[wangliyuan72]

Need SILVA ref alignment to align our sequences from the rrnDB so that we can make sure we are looking at a consistent region within the gene. We can get this from the mothur wiki. We would like the recreate SEED database from Release 138.

• https://mothur.s3.us-east-2.amazonaws.com/wiki/silva.seed_v138_1.tgz

Put this into data/references