Restructure and cleanup

Moved a few things around:
 * multimedia
    No longer exists, since the `detect-dvd` script that was contained in it
    is an XFCE4 specific thing, and has been merged with the `xfce4` directory
 * firefox, thunderbird
    In a separate directory `applications`
 * xfce4/gedit-plugins
    gedit plugins are not really part of Karoshi, and so have been removed.
 * xfce4/gvfs-mounts
    Moved into two nested directories: xfce4/gvfs/mounts

All scripts have had the Makefile message at the top modified to fit more with
how autoconf does it (@configure_input@) and how other Makefile-passed
variables are declared: @makefile_in@