move .gajim to XDG_CONFIG_HOME
Problem
freedesktop.org has a specification for X window system applications: http://standards.freedesktop.org/basedir-spec/basedir-spec-latest.html, while Gajim uses plain .gajim for its preferences and files.
Enhancement recommendation
It is better to move configuration files to $XDG_CONFIG_HOME (.config/ by default) and user data files such as logs to $XDG_DATA_HOME (.local/share/ by default).