Interactions scrolling + containment

@scottgonzalez @mikesherov Here are a lot of changes to fix scrolling and their unit tests. There were several issues with fixed-position draggables. 

The biggest problem was not testable via qunit ( it would move to right spot but mouse would appear off in browser ). I ended up figuring multiplying by 2 magically fixed those elements, no matter the size of the element. I don't know why and that scares me.

I also made test helpers use `position` rather than `offset` so fixed position would work.
Scrolling tests when using `clone` were broken because they used multiple moves, didn't `setScroll` properly. The result,expected was in reverse as well.

Looking forward to getting this merged - all tests not having to do with other interactions seem to be working now.