Draft: Flint: Stat widget in live curve plot

Closes #3373

This MR is a check to try to integrate the default silx stats widget into Flint.

It sounds like it works but

• It is unstable, and can segfault when we open/close the window.
• For the Flint use case, it is probably better to display the statistics vertically.
• The legend have to be patch because we use a mangled name which was not designed to be read
• It is not possible to display the statistics for all the curves, because FLint recreate new item at every frames, and the widget do not handle properly that behaviour.

As result it could be easier to just redesign our own widget for that.