[sgala] check autoaway state only every 10 seconds, so that gajim allows for processors to sleep longer for power saving (see linuxpowertop.org)

prevent a TB when a jid is in mem but not in DB (is has been removed while gajim was running) fixes #3073

 * improve account context menu
 * improve groupchat user's context menu
 * improve group context menu
 * improve join groupchat menu

 * Improve coding of [8220]

[omega] Don't check the fingerprint of the SSL certificats with a fixed list, but use OpenSSL to check if the certificat is valid.