Delay DNS-SD queries and improve network printer management

Previously DNS-SD queries for printers were done immediately after network connection came up. In some cases this turned out to be before NetworkManager had done new DNS settings which caused the queries to fail. The script has now a --delay switch that makes it sleep before doing the queries. The script is now run in the background with the delay which seems to work much better.

Printer management is changed so that printers listed in /var/lib/puavo-desktop/dnssd_printers are used only during deleting printers. When querying and adding printers, lpstat is used to find a list of current printers. This fixes cases when user had deleted network printers from cups as the old version did not notice that the printer was missing.

/etc/cups is also linked as a whole to /state as cups seems to create a completely new printers.conf file instead of modifiying existing file. Previously only /etc/cups/printers.conf was linked to /state which caused the printer settings to dissappear.