print-notifications: Move translator comments to appropriate positions

Move translator comments 1 line above the actual strings so that
translators see them.
print-notifications: Coding style fixes
print-notifications: Use better debugging messages

Using g_debug() is more appropriate than gnome_settings_profile_msg()
for message about getting dests from CUPS server.
Be more specific in those debugging messages.
print-notifications: Honor CUPS' default port number

Don't default to "631" for default port when testing connection
to remote CUPS server.
print-notifications: Connect to message bus asynchronously
print-notifications: Cancel subscription to DBus signals when finished

Store id of the subscription to CUPS' DBus signals and remove it
when stopping manager.
print-notifications: Stop renewing of CUPS subscriptions once we are finished

Store id of the event source which renews subscriptions and remove it
when stopping manager.
print-notifications: Don't use DBus recipient URI for remote servers

Using DBus for notify-recipient-uri is useless for remote servers.

https://bugzilla.gnome.org/show_bug.cgi?id=678623
print-notifications: Don't run connection test for local server

https://bugzilla.gnome.org/show_bug.cgi?id=678623
print-notifications: Use IPP method for getting IPP notifications

Use method IPP_GET_NOTIFICATIONS for getting of IPP notifications
instead of relying on DBus interface of CUPS. This change allows
us to unify getting of notifications for remote and local CUPS
servers later.
Use DBus notification for signaling the need for getting of new
notifications.

https://bugzilla.gnome.org/show_bug.cgi?id=678623
print-notifications: Regularly check for notifications from remote CUPS servers

Get new notifications every 60 seconds if the CUPS server is a remote one.

https://bugzilla.gnome.org/show_bug.cgi?id=678623
print-notifications: Show final job states for remote CUPS server

Remote CUPS servers send information about final state of print jobs
in job-state-change event instead of in job-completed event.

https://bugzilla.gnome.org/show_bug.cgi?id=678623