Dear maintainer

So I have developed a PyQt application with matplotlib in the past and now I wanted to try it with Gtk because prettier (in my humble opinion) and probably easier on the dependencies.

However, I very much miss the "edit parameters" button on the Gtk toolbar, which is present on the Qt toolbar. I would very much like it if this button is also implemented for the Gtk backend or preferably straight into the matplotlib.backend_bases.NavigationToolbar2 class, because I also miss the "edit parameter" button when using pyplot for quickly hacking a graph together.

Thank you for matplotlib, I love it!