Only save molecules back to archives if changes are made

[karlduderstadt]

We should keep track of whether anything was changed in records before calling put to return molecule records to the archive. In the case of virtual archives the put method triggers saving of the record back to file, which can be time consuming and is not needed if you are quickly just looking through traces. Checking first and only saving if something changed could improve performance.

Another option would be to delegate the saving to a background thread, however, how then should we handle the case where someone goes forward on record and then directly back to the previous record before it is done saving? This can all be done, but would take some work. First we should try and only save if changes are made, this would catch most use cases.