- on construction of a KIWIXML instance, return early if no
  pointer to the image configuration directory is defined
- Use isolinux to boot an install CD
  + Instead of using the bootloader selected for the image raw
    disk to boot the install iso we use isolinux which is the
    correct loader for an iso. In addition this now also allows
    to create hybrid install iso images
- Update all JeOS templates to include the gfxboot-branding if
  the selected image type is "oem". This is done to have a graphics
  boot menu for install iso images