Some notes when you want to use onboard without GNOME

run something like these:
eval $(dbus-launch)
onboard &

you want to install these:
onboard dbus-x11 gir1.2-atspi-2.0 gsettings-desktop-schemas
at-spi2-core dconf-cli

and play with these:
gsettings list-recursively org.onboard
