Modify desktop-defaults-run to:
1) Remove configuration option for enabling the session filemanager override
2) Add command line option to follow (--follow) the session filemanager
   Example: desktop-defaults-run -fm --follow
3) Add desktop-defaults-follow-fm.desktop
4) Change default links to default programs (set default defaults)

There is no longer a need for /etc/desktop-session/desktop-defaults.conf and it
can be safely removed
Removed old configuration file