activate as in Gtk::CellRendererToggle

[Germán Diago <germandiago gmail com>]

Hello. I'm trying to use an embedded button in a treeview.
I managed to get that working. But now I want the button to be activatable.
There's an activate member function, but there's no signal_activate to
connect to.

Is this because I have to generate it myself? How can that be done? I
don't know
very well how to approach the problem. Thanks.