re-work of debs, config, scripts handling, according to issue #715

re-work of debs, config, scripts handling, according to issue #715

- debs, config and scripts are always searched and read from the
    same place ($dcs-dir). Which place this is varies, depending on
    GRMLCFG, noautoconfig and myconfig.
  - debs are searched in $dcs-dir/debs. If debs=foo is given, foo is
    taken as a shell wildcard for the debs being installed, paths are
    allowed and relative to $dcs-dir.
  - config archives (config.tbz) are searched directly in $dcs-dir. If
    config=foo is given and foo is a file, that file is unpacked and its
    content taken as configuration archive. If config=foo is given and foo
    is a directory, the contents of the directory tree is copied over the
    live CD configuration. paths are allowed and relative to $dcs-dir
  - scripts are searched in $dcs-dir/scripts. If scripts=foo is given
    and foo is a file, that file is executed. If scripts=foo is given and
    foo is a directory, all files inside that directory are executed.
    Paths are allowed and relative to $dcs-dir.
  - If no GRMLCFG partition is found and noautoconfig is _not_ given
    on the command line, nothing is changed and the dcs files are
    searched within the .iso, $dcs-dir is set to the root directory
    within the .iso
  - If a GRMLCFG partition is found, $dcs-dir is set to the root of
    the GRMLCFG partition unless noautoconfig is set. If noautoconfig is
    set, $dcs-dir is set to the root directory within the .iso.
  - If myconfig=foo is set on the command line, $dcs-dir is set to
    foo, even if a GRMLCFG partition is present.