Adds unit test to verify #1153 bug with ArrayController range observer + orderBy.
Fix the content change notofications for array controller using orderBy.
If the controller is sorted (via an orderBy) and new items are added, the ordered sequence may change so we need to trigger a notification for a full UI refresh. If only removing items (added == 0), the order of remaining elements is not changing therefore no need to perform such a full refresh
Tweaks comments on range observer fix.