Add dot plot comparing categorical and categorical 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) ~ categorical (1) features
e.g. predicted cell type vs. annotated cell type. This plot is particularly useful when there are a lot of categories.

The above is an example of categorical (y) ~ categorical (x) dot plot. Here the shade of the dot and radius size are both defined as given a single row category, the percentage of column category. Again here the color scale should be decided. Legend is not shown but needed in the example above.

This is essentially the same data in the bookmark here. But a different view.

Options:
x and y can be swapped in display, because due to what the dot shade and radius means, this is not a simple swap of axis, the values need to be re-computed.