Prevent traceback when gajim-remote is used while gajim is not running. Add a check_gajim_running command to gajim-remote

See #3718. See also [9287].

Merwok complained about left and right arrow on tab in chats couldn't allow him to do traversing. This patch is a almost there fix. What is missing after the new tab is focused, it steals focus [couldn't find how to fix that atm], hopefully Yann remembers nicfit's code better..

Do not redraw roster when opening the accounts window. Rework preference window. Fixes #3330, #1621, #2113

add checkbutton to YesNoDialog. Ability to fall back from tls to ssl and then plain. Warn user when using insecure connection. fixes #1923

[sgala] nicer code. No need to change contact's status to offline when we go offline if contact is already offline. see #3718