Added wasChecked option to persist checked state

Persist the checked state of radio / checkbox.  Can be used with localStorage or cookies.
Here's an example using jquery-total-storage plugin - https://github.com/jarednova/jquery-total-storage:

    $('#somediv').simpleImageCheck({
        image: 'unchecked.png',
        imageChecked: 'checked.png',
        wasChecked: $.totalStorage('checked'),
        afterCheck: function(isChecked) {
            if (isChecked) {
                $.totalStorage( 'checked', 'true' );
            }  else {
                $.totalStorage( 'checked', 'false' );
            }
        }
    });