Support for statistical annotations

[mchaniotakis]

Often when biologists draw a plot to compare data, statistical analysis along with the statistical annotation of the p-value comparison on the graph is a crucial step. Can this feature be implemented? If so, and if there is help needed, I would be more than happy to help out with this feature. Here is an example:

[ObservedObserver]

Status update:

It seems still a hard issue here.

1. vega-lite is not well designed for annotations. (small problem, we are able to make it.)
2. How to make annotation general enough for all visualization cases with no-code GUI. Usually, engineers make a chart system for this, and add a new chart type with a special config for annotation. But I don't want graphic-walker/pgwalker to become a chart system which you select a chart type and config it. I want it to be general enough that there is no concept of chart, but basic elements of graphics (like mark, visual channel, coordinate, scale, etc)