Colorize the minimized DDT icon

[d9pouces]

I made an extension to check the HTML validity.
However, my DDT is minimized and I don't see the result.

Why not add a method get_warning_level (0/10/20/30/40/50/… like the logging module) to the Panel class?
The minimized icon could be colored following the maximum level (across all panels), being red if any panel is above 40, orange if any panel is above 30, and so on.

For example, the SQL panel could raise a warning if there are too many requests or if there are too slow or the Django panel could be red if the current Django version is not supported anymore.