once for all the items to be removed, passing in their list as argument. This method,
and the method Clear calling it, are used for alerts, updates, events and connections,
hence changed the handling of the CollectionChanged event in these cases to expect
either a single item or a collection. In the case of alerts, updates and events
this means that we can rebuild the whole list instead of removing single rows which
causes the application to hang for big numbers of items.
