MAINT: new DADA2, new PD Mice guidance (qiime2#492)

MAINT: otus->features in artifact api tutorial (qiime2#483)

Apply suggestions from code review

Co-authored-by: Chris Keefe <39198770+ChrisKeefe@users.noreply.github.com>

DEP: scikit-learn 0.22.1 (qiime2#449)

MAINT: SEPP-refs production-mode (qiime2#438)

Revert "MAINT: drop BIOM v1.0.0 (qiime2#427)"

This reverts commit 3e0bf80.

MAINT: Moving pictures updates (qiime2#404)

- DADA2 1.10
- Misc grammar

MAINT: New feature classifiers, 2019.1 (qiime2#385)

BUG: Remove missing doc page comments (qiime2#367)

MAINT: Update install guide; New copyright year (qiime2#284)

Fixes qiime2#279
Fixes qiime2#283