text: Title: Make `plot_config` and choice of renderer a global config 
  Body: As described [here](https://lux-api.readthedocs.io/en/latest/source/guide/style.html#styling-custom-plot-settings),`plot_config` is used for setting the plotting style for the rendered visualization. Currently, this is a property that is tied with the dataframe, we should extend this to make this a global config setting (e.g., `lux.config.plot_setting`). The configuration is dependent on the choice of renderer too, so it makes sense to have this as a global setting.