Updated responsive/breakpoints option to work with slickSetOption.

When working with `.slickSetOption`, I realized that it was ignoring any `responsive` options that were updated and set. This code change manages to fix that along with allowing `.onBeforeSlide` and `.onAfterSlide` to be used in that `responsive` option.

Originally, `.slickSetOption` was completely ignoring the `responsive` options, and `.onBeforeSlide` and `.onAfterSlide` were not being updated on page load, only when the viewport was being resized.

I'm a little iffy on this fix so any feedback would be helpful! Thanks.