activate panel on scroll even when snapping is disabled

Panel activate event and any corresponding menu's now respond to scrolling even when snapping is disabled.

You can see an example using my fork in this **[Plunk](http://plnkr.co/edit/jncx8lB4xpVjmj7I5Gro?p=preview)**.

We may want to play with some kind of additional threshold here as well.