JavaScript on page load and on scroll functions
I can't really see much to refactor in your code except a few things, so I'll go through those.




if (trigger_height == false)



could be if (!(trigger_height))




$this = $(this);
if (isScrolledIntoView($this, false)) {
    $this.removeClass("hidden");
}



I don't really see why you need to initialise $this, you could just use $(this) later on instead.