Add new attributes for devices:

* puavoPrinterDeviceURI
* puavoPrinterPPD

with school/organisation fallback:

* puavoAllowGuest
* puavoPersonalDevice

Printer information is used to always configure a local printer on
diskless workstations for local usage.

Setting puavoAllowGuest allows guest users to login to the device
without having any kind of user credentials.

On personal devices users have more freedom to do local configuration
changes that affect also other users. For now this includes wifi and
printer settings.