ENH: heatmap: support row_colors and feature metadata annotation on plots

[nbokulich]

Current Behavior
Currently supports label annotation of sample metadata information.

Proposed Behavior
Please allow the same for features. And please support annotation with row_colors and col_colors instead of or in addition to label annotation. E.g., see the following plot from the seaborn clustermap docs.

E.g., color by phylum affiliation. Allow level selection from semicolon-delimited feature IDs? This would be useful for taxa but also, e.g., KEGG annotation.