Radar plot basic

Referencing issue #982 
Should cover the first 5 points of that issue.

Note: branch targeted to radarPlot as a feature branch
Note: only one dataset can be added and while a dataset can have multiple datums, a single datum is the only tested behavior on my end.
hmm if metrics is the name we wanna go with (as opposed to, say, `keys`) then please reference it in the constructor.