Better solution for KoDocumentInfo and content in documents.

When changing the current author we only update the KoDocumentInfo if the document has been
modified or is empty.

On first modification we make sure the KoDocumentInfo reflect what the author profile says

This makes sure we can work as a viewer still, showing the last author, but as soon as the user
starts to edit the document the document info/textvariables are updated.

It may sound simple, but it took some soul searching to convince me this is the right approach.
Well that and thinking of the best way to implement it.

What this patch does NOT do is update the current author selection menu when new author profiles
are created, and document also doesn't reflect changes to current profiles. This is because by
design the author profiles are shared across all calligra applications, so in order to accomplish
this we need to listen to changes to the config, and call KoDocumentInfo::updateParameters().