Add dot plot comparing categorical and continuous features

[MillenniumFalconMechanic]

From original requirements doc:

Xena chart is implemented using the Highchart library. Highchart has a bubble chart mode (https://www.highcharts.com/demo/bubble).

Dot plot comparing categorical (1) ~ continuous features (>1)
e.g. a panel of gene expression across a set of different cell types, particularly when there are a lot of genes or categories)

The above is an example of categorical value (y) ~ continuous value (x) dot plot. Here the dot radius and the shade of the dot both represent the average value of the continuous feature in the corresponding category. The color scale needs to be decided.

This is essentially the same data as the bookmark below, but a different view that only shows mean/average, not distribution https://xenabrowser.net/heatmap/?bookmark=2e9f881e6a18197ddc548f12df3f9b5e

Options
x and y can be swapped in display.

Advanced options
Continue feature value transformation, these are essentially the same as the options in bookmark above, but the wording needs to be modified from "y unit" to "continuous data unit", "y data" to "continuous data". This is because the continuous data can be on the x or y axis, depending if they swap the axes.