Clean "~/.cups/lpoptions" file before setting default printer
on local CUPS server. Store default printer to "~/.cups/lpoptions"
if we are connected to a remote CUPS server (#646100).
This patch makes Printers panel to automatically refresh printers list
when a new printer is added or removed. It is refreshed also when a printer
changes its state (to see changes in paused/unpaused state) (rhbz#691718).
It also automatically refresh list of jobs (and also number of active jobs in
main tab) for actual printer (rhbz#691737).
The dialog is able to add printers discovered by cupsGetDevices().
It can also add printers from a remote CUPS server by typing
its address and selecting printer we want to add (#640734).
