[gtkada] tick_label signal

[manuel.op.de.coul at eon-benelux.com]

I wrote:
>And I'd like to make a plea for a provision of To_Marshaller
>for the "tick_label" profile in Gtk.Extra.Plot in the next version.

Whoops, I figured it out now, not necessary.
I think my handler for tick_label would make a nice example for
the documentation! Then no need for others to reinvent it.

Manuel