Fix blinking regulation plot legend

Closes #2743 (closed)

This MR fix the blinking of legend displayed by the plot of the regulation controller.

This was done by removing the fig.clear_data call.

This clear_data was only introduced as a work around for a memory leak created by matplotlib. It was subsequently fixed with a matplotlib monkey patch which is setup by Flint. As result clear_data can be removed without problem.

This MR also introduce a regulation mock to the demo session. So what people can play with.

Plus small fixes.