For each knowledge document in powerKNOW the history of the document can
be recorded. If enabled the document history contains the following informations:
Date + time when a change to the documents contents or to it's status has been made.
Status to which the document was switched
Info whether a change has been made to the contents.
(This is strictly a yes/no info. The old contents is NOT held for comparison).
User who has made the change.
Recording and showing the document history is configurable. Configuration is done
with the config key 'documentLogLevel'.