rename amplicon16S_analysis to classify_qiime2_multi

[dpark01]

I've been increasingly thinking that maybe we should rename our new 16S workflow to be more consistent with the naming schemes of other WDL workflows we have in here. classify_qiime2_multi would fit the verb_toolname_entitytype naming scheme we have for a lot of our workflows already.

The thing that makes it discordant from all our other classify_xxx workflows is that it doesn't emit 1) krona plots, 2) kraken-style summary reports, or 3) kraken-style per-read taxid assignments. But that's okay, especially since it looks like 1 is not hard to add with the right plugin and even if we didn't add that functionality, it would at least help bucket the workflow with the right family of related workflows.