Enabled scroll-glue to work on the body element.

Hi,

I made scroll-glue work on body elements. In that case you've to register on the `window.onscroll` event. The calculation in `shouldActivateAutoScroll()` is a bit different to normal elements, too.

I tried to create karma tests for the extended behavior, but if I understand it correctly, the compiled templates will be appended below the body element. That would result in two nested body tags, which obviously doesn't work.

Kind regards
Marcell