Rewrite Dot Plot

[yihangx]

The way dot plot is currently implemented, it's a glorified scatter plot with large circles. What we would want is the ability to map a gradient color (or size) onto the circles to reflect a value. There are three potential inputs: X axis (could be a string or nothing), Y axis (could be a string or nothing), dot value (must be numeric). If I don't provide an X axis, we get a vertical dot plot with one row. If I don't provide a Y axis, I get a horizontal dot plot. In either case, just like in the case of a heat map, we would want to map a color, but we also might want to vary the size (or both).