The default of 32 px should be fine in most cases and when the UI is scaled
it is also automatically scaled. However, if one has a tray area or Plasma
panel with extraordinarily big icons like latte-dock it might still be
required to render icons at a higher resolution. This is hard to determine
programmatically so I'm just adding a manual setting.
This is useful because sometimes the background color of the system
tray is dark but the overall system UI still uses a light theme.
For the Plasmoid this should never be the case, though. Hence the
extra settings are not available there.
Martchus