printers: Don't update alignment padding for dialogs

The update of alignment padding is not needed since gtk+ 3.14.
It was needed for proper alignment of widgets of action area
with those from content area.

https://bugzilla.gnome.org/show_bug.cgi?id=739737
printers: Don't use methods of deprecated GtkMisc

Use GtkWidget's methods for settings of halign, valign and margin-start
instead of GtkMisc's methods for settings of xalign, yalign and xpad.

https://bugzilla.gnome.org/show_bug.cgi?id=739737
printers: Add GtkLabel with printer model name

Place a custom GtkLabel with name of printer model
into "printer-model-button". This is needed for us to be
able to align the text and keep the button filling all available
horizontal space.

https://bugzilla.gnome.org/show_bug.cgi?id=739737
printers: Fix padding of a progress text

Set padding of the text "Setting new driver" at runtime so that
it is aligned with other fields properly.

https://bugzilla.gnome.org/show_bug.cgi?id=739737
printers: Remove usage of deprecated GtkAlignment

Use halign and valign of children instead of adding
GtkAlignment and setting of xalign and yalign.

https://bugzilla.gnome.org/show_bug.cgi?id=739737
printers: Don't use properties of deprecated widgets

Replace xalign and yalign properties by halign and
valign wherever needed.

https://bugzilla.gnome.org/show_bug.cgi?id=739737
printers: Fix spacing in Jobs dialog

Increase spacing in the VBox to 10 as in other dialogs.

https://bugzilla.gnome.org/show_bug.cgi?id=739737