GPII-364: Added an onOffSwitch template.
This is used in contrastEnabled adjuster. Uses Alex's code and needs some renaming.
GPII-364: Renamed the elements' classes and IDs in onOffSwitch.
GPII-364: Created a reusable onOffSwitch adjuster component.
GPII-364: Tweaked a bit the onOffSwitch style.
Will need some more work here...