Sticky SideWidgets on scroll

[iamdarkle]

I think it's a good idea to keep SideWidgets on scroll to avoid having to scroll all the way to the top to change categories. It's something I'm currently using on my site (if you want to see a demo) via CSS but maybe it could be incorporated by default.

Let me know what you think to close this issue in case you prefer not to incorporate it as default 😃