virtual-scroll: design interaction with router

[mmalerba]

Design how virtual scrolling will work with the router.

How will we make it easy for users to scroll back to the right location when the user leaves the page and then presses the back button?

[amcdnl]

In my implementation, did the following:

• Set the id of the item selected in a route param
• Listen to the router events
• When param changed, use a scrollToItem method to scroll into view