Prevent triggering callback functions on page load

In original SwitchButton, the callback functions are triggered on page load. In our requirement, on page load, it was triggering the callback such that all button's status is updated to server.

We wanted our application to initially load the data and update server ONLY when turning ON or OFF.

We added a flag trigger_callback_onload which is true by default to keep the current behavior and when the button is initialized with trigger_callback_onload as false, it will not trigger callback on page load