2163: don't create a new subtitle version when tasks are approved

This change replaces the old code that always created a new version with new code that simple changes the visibility of the current version to public.

One difference is that before we would be able to set the author of the version to the reviewer/approver, rather than the original owner.  However, if the reviewer/approver makes any changes then we create a new version anyways.  So this only matters in the case where no changes are made.  Still I'm not 100% sure that this is correct.