This adds an 'animateItems' option that, if set, will fade in newly

added items and fade out removed items. This can be controlled by the

'animate' option when adding/removing items, and will default to true if

'animateItems' is turned on.

Tested with an in-progress change and animation turned on. Saw the items

fade in when newly added and fade out when removed.
Tested that existing configform lists weren't animated.