GNOME Settings Daemon has been split up into separate daemons,
which means we'll need to invoke those separately.

See https://git.gnome.org/browse/gnome-session/commit?id=18b6e567e1a
for the corresponding change to the regular session file.

These files are used by gnome-session and it does not even read
Name from *.session file.

https://mail.gnome.org/archives/gnome-flashback-list/2015-August/msg00028.html

https://bugzilla.gnome.org/show_bug.cgi?id=709016

Add new gnome-flashback-init application that will be autostarted
in Initialization phase. This will allow as to set some session
environment variables.

Currently it will be only used to set XDG_MENU_PREFIX.

Initially this application does nothing.