GPII-724: Fixed problem with on/off switches always being reported as unselected from NVDA.

Link to JIRA: http://issues.gpii.net/browse/GPII-724

The screen reader now reads,
"Speak text checkbox not checked"
when the on/off toggle is off and,
"Speak text checkbox checked"
when the toggle is on.
Note that this change has been applied to all on/off switches since this is happening in the reused grade "gpii.adjuster.onOffSwitch".