GPII-364: Created the addContrast adjuster as a composite panel.
This will be the container for all adjusters of "add contrast" group.
Trying with highContrast adjuster as member of the composite panel but
with no success.
GPII-364: Cannot make the highContrast adjuster work as composite.
Temporarily made highContrast checkbox visible for testing purposes.
The contrast label is not in the composite base.