Since `ChartPlotWidget.update_graphics_from_flow()` is more or less just
a call to `Viz.update_graphics()` try to call that directly where
possible.
Changes include:
- calling the viz in the display state specific `maxmin()`.
- passing a viz instance to each `ChartView._set_yrange()` call (in prep
of explicit group auto-ranging); not that this input is unused in the
method for now.
- drop `bars_range` var passing since we don't use it.
81ccc14c98