bootserver: script for updating tftpboot dirs with image kernels

It is basically a simplified and cleaner version of ltsp-update-kernels,
but it is NOT a drop-in replacement: it has a different name and uses
different environment variables (PUAVO_IMAGE_DIR and
PUAVO_TFTP_BOOT_DIR).

Use --help to get help.
client: Add intel-backlight hack also for HP Probook 430 G1
client: Add a new lightdm greeter-setup setup script to set keyboard
layout when the greeter starts.
client: Add a new lightdm greeter-setup setup script to set keyboard
layout when the greeter starts.
Merge remote-tracking branch 'origin/master' into trusty

Conflicts:
	client/Makefile
	client/templates/etc/lightdm/lightdm.conf