random forests classifier

Some examples to consider:
- EMPO categories -- How well can we predict the EMPO category at multiple levels? (Zech did this already)
- ENVO categories
- Soil geography -- Can we predict where a soil is from based on its microbiome? (need to control for soil type, pH, other confounding factors?) @gilbertjack ask about this.

No file, test, or entry point is named. Start by reviewing the proposed EMPO, ENVO, and soil-geography prediction examples and the referenced prior work; done requires a decided prediction scope and an implemented, evaluated random-forest example with confounding factors addressed where relevant.

Written by the indexing model from the issue text.