v1.6.0

- rename phone.mk -> mobile.mk, drop feature phone
- live: refactoring 60-live-rescue-root, add autologin root to serial tty
  in rescue mode
- efi: add mockutil, pesign to rescue only
- Add VERSION file for build doc
- doc: do not use images from asciidoc, add missing images (fix FTBFS)
- mediacheck: show "Error: implantisomd5 is not available" on screen
- grub, syslinux: add lowmem to 25install-vnc-* also
- Add support patches from image-paches.d/
- Set MKI_VER_MINIMAL=0.3.0, MKI_VER_OPTIMAL=0.3.2
- fix some package lists