Move resolveTooltipFormat() (and add resolveFormat()) from ALabel down into
AModule, and add a generic updateTooltip(Gtk::Widget&, ...) helper. This lets
modules that are not ALabel-derived reuse the shared tooltip logic instead of
re-implementing it. Migrate gamemode (the only non-ALabel module reading
tooltip-format) to updateTooltip(box_, ...). ALabel inherits the resolvers.