Timeline diffview for latest item is incorrect due to sorting of properties in metadata

[DonJayamanne]

Does this issue occur when all extensions are disabled?: Yes/No

There are no differences in the timeline (this is the very last entry in timeline)
However diffs are displayed due to the order of properties in metadata differing

[DonJayamanne]

Its a problem with JS stringify, the order of property is preserved (ie. the order in which they have been added)

[DonJayamanne]

Do we need an API in ipynb extension to add/update metadata to get around this?
Or just write custom code in each ext.

Note: Serializer ext needs to ensure properties are always sorted
Problem with 3rd party exts that update these objects

[DonJayamanne]

Done