listener when last there are no more senders

the recipient

save last dir used for emoticons, sounds, sending file, recv files in config and if empty use $HOME. no more bad paths (the dir were we started Gajim, no more saving such info only per session)

last_send_dir for sending and not last_save_dir for sending! also os.path.isdir() is enough and no need for exists() and last but not least set $HOME if last_*_dir is None (else we show the place from we run Gajim!