WebComment: deleted record message

* When trying to display comments from a deleted record,
  inform the user that the record has been deleted instead
  of replying that the record does not exist (in '/comments'
  tab) or displaying no output ('yourcomments' page).

Signed-off-by: Jerome Caffaro <jerome.caffaro@cern.ch>
Tested-by: Tibor Simko <tibor.simko@cern.ch>