Bug#1002845: onboard: the status icon does not appear on gnome

[Teodoro Coluccio]

I have found a solution, at least as far as the use on gnome is concerned.
This consists of
a) install the gnome extension AppIndicator and KStatusNotifierItem Support 
from https://extensions.gnome.org/extension/615/appindicator-support/.
b) in the onboard settings, in general, you need to set "status icon provider" 
to "AppIndicator (Unity, KDE)"
c) Finally it restarts (even a logout is enough).
In this way, the onboard icon will correctly appear in the top bar of gnome.