Follow XDG Base Directory specification and use $XDG_CONFIG_HOME/geany (most often this is ~/.config/geany) as default configuration directory (closes #2166229).
The previous configuration will be moved to the new location if the new directory doesn't exist yet.
Move utils_make_settings_dir() into main.c.
Remove win32_get_appdata_folder() because g_get_user_config_dir() does the same.

git-svn-id: https://geany.svn.sourceforge.net/svnroot/geany/trunk@3219 ea778897-0a13-0410-b9d1-a72fbfd435f5