Uploadpdf - resend updates if no reply within a time limit

Sometimes when editing a comment the update message to the server can get lost.

All requests, which do not receive a reply, should be re-sent after a timeout (with appropriate annotation to indicate that it is a repeat message, so the database should be checked for duplicate entries, if this is a 'create new comment' message; 'update comment' messages should be safe to re-apply).