installer: rework buildscript

Signed-off-by: Stephan Raue <stephan@openelec.tv>
projects/RPi/patches: add patch needed for NOOBS support

Signed-off-by: Stephan Raue <stephan@openelec.tv>
scripts/image: add initial NOOBS support

Signed-off-by: Stephan Raue <stephan@openelec.tv>
bcm2835-bootloader: update to bcm2835-bootloader-3ab17ac

Signed-off-by: Stephan Raue <stephan@openelec.tv>
CHANGELOG: update changelog

Signed-off-by: Stephan Raue <stephan@openelec.tv>