Better fix for the problem causing Critical assertions in
gtk_adjustment_set_value/page_size and g_object_freeze/thaw_notify.
These resulted from calling gtk_databox_set_total_limits()
in gtk_databox_init(). Setting only the box->priv->total_* led
to a nasty bug caused by translation_factors being calculated to
infinity values, resulting in no graphs being shown. By setting
box->priv->visible_* also to a rational default, everything works
better. This is not the definitive fix. Should figure out why
translation_factor got screwed up in the first place.