bootserver: update DNS records required by airprint after ddns init
bootserver: update airprint DNS records once per 15mins

This ensures printer permission/visibility changes in Puavo come into
effect with max 15min delay.

This kind of recurring and stupid update-loop is required until
bootservers can subscribe to Puavo event queues.
bootserver: install airprint DDNS update cron script
bootserver: fix trivial typo in airprint update cron script
bootserver: Set LANG=C before calling ifconfig as the regex that scrapes
the information otherwise breaks if the content is localised.
client: Remove 50-default-display-manager as it was needed for ldm
and it messes up normal lightdm startup through upstart.
client: Import files from ltsp-lightdm to get rid of ltsp-lightdm
package.
client: Rename puavo-desktop-guest-session -> puavo-desktop-session
client: Start lightdm through Upstart instead of screen.d/lightdm
script.
client: Conflicts with ltsp-lightdm as some files have been moved
to puavo-ltsp-client instead.
client: Add support for webkiosks that run only guest sessions. Guest
session is started automatically from lightdm and language selector
asks the user for language. When the language is selected, the session
locale is set and xautolock is started automatically to kill the session
after 10 minutes of inactivity. The session still needs to be cleaned
so that webkiosks do not have reboot/shutdown/password change buttons.
Start using the new webkiosk-language-selector package.
Fixing typos..
Automatically start firefox for webkiosk users.
Use "elif" in 41puavo-set-locale when setting LANGUAGE,
the shellish way of writing "else if".
client: Call LTSP's /usr/share/ltsp/screen-x-common script to
configure xorg using lts.conf.
client: Use 16-bit screen depth on thinclients.
client: puavo-desktop-session is now used also on laptops, so run
gnome-session on them too.
client: Fix lightdm system service starting / removing on different
device types. lightdm upstart script should be kept on thin/fat clients
and laptops and removed on other devices.
Read /etc/puavo/device.json in puavo-configure-client.
This code is actually by Veli-Matti Lintu from no-ltsp-lightdm
branch, but I take this now here because I need this for
another purpose.