Add initValue

According to this thread, i have added an initValue that can set between 2 steps. after the first initialisation the initValue will never reached again because the "value" is added or subtracted with "step"

the initialisation look like this:

$( ".slider").slider({
                step: 10,
                min: 10,
                value: 35,
                initValue: 35,
                max: 60
});