qiime2 plugin

[mortonjt]

We should to try to stick with the q2_sample_classifier plugin standards as much as we can - possibly even have it as a dependency.

Right now, we are using objects from q2_sample_classifier. Relevant to qiime2/q2-sample-classifier#207

Upcoming subcommands

• finetuned-classifier : builds q2 classifiers using the big model as a scaffold
• knn-classifer : builds q2 k-nearest classifier