Add index to iteration view

Fixes #575 

@angelini suggested a simply way to add an index property to the iteration view. Unfortunately it doesn't work correctly because our collection events do not consistently include the indexes of the items add/removed/moved.

Throwing this PR up with some broken tests to start a discussion on this. I have not dug into why the events do not fire with the indexes provided. Is there a reason for this, or is it simply an oversight?

@nickjs @pushrax @angelini