Not all potential groups found when generating unsubscribe list

Following a discussion with TIm it was thought that when we check for the entity type of included items e.g. mailing or group, with the current code for the unsubscribe function we only get 1 type back. However a mailing could be made up of multiple .e.g. past recipients of a mailing and group(s). So it seems sensible to alter the code to try to check for all the possible permutations