feature: make the scrollView scroll to top and show the contentView

When the scrollView's content is larger than the scrollView itself and forcing reload with `[self.pullToRefreshView startLoadingAndExpand:YES]` the view is not expanded (setting the insets is not enough). This patch checks if the scrollView is at top and does the scrolling. I'm not sure that this is done the correct(tm) way, but I think it's the intended behavior.