Add ../collections/<collectionKey>/items/top

../collections/<collectionKey>/items now returns both parent and child items.

(These apply to the new API only. The old API doesn't include child items within collections.)
Make sure item/collection updateFromJSON() is in a transaction
Include full errors in write results on testing site
Make sure item timestamp gets updated on API writes

Previously, the timestamp wasn't updated when changing an attachment note, and probably in other situations.