Provides a saveUI pipeline implementation to prevent unintentionally overwriting a changed serialized item on disk. For example, if user A changes an item, then user B pulls that change from SCM but does not sync it into Sitecore, then user B changes that item, without this handler user A's changes would be overwritten. This handler verifies that the pre-save state of the item matches the field values present in the serialized item on disk (if it's present). If they dont match a sheer warning is shown.