Add autoiso.cfg and osdetect.cfg support

With autoiso.cfg, you can drop any loopback-enabled ISOs "at runtime" into
/grml-plus/ISOs and they will be detected on the next boot if you choose
the autoiso option. BIN and IMG and CFG files are also detected.

Also add osdetect.cfg, which can be used to detect operating systems on
hard disk and boot from them.