Set 'PageSize' instead of 'media' for new printers since we use PPD
for construction of the combo for selecting of default paper size.
Previously, we've been setting 'media' attribute for new printers.
Attribute 'media' is used by IPP but we set paper size using 'PageSize'
which comes from PPD in the options dialog. Sometimes (quite often) IPP
gets priority over PPD in print systems. Therefore there was inconsistency
of what user set as default paper size on the options dialog and what was used.
Also don't mark IPP and user's local options as default in PpPPDOptionWidget
since it should use just PPD (we can change PPD values only in this widget).
Since we use PPD for setting of paper size in the options dialog, we shouldn't
show a value which user does not change actually (IPP's 'media' vs. PPD's
'PageSize').
https://bugzilla.gnome.org/show_bug.cgi?id=748569
Set 'ppd_filename_set' and 'destination_set' always to FALSE
before requesting the destination and updated PPD file so we can
distinguish when we have all information needed for update
of the PpPPDOptionWidget.
https://bugzilla.redhat.com/show_bug.cgi?id=1211580
Use GCancellable when setting a new value of an option.
This prevents Printers panel from crash caused by
calling of option widget's callback on finalized widget.
https://bugzilla.gnome.org/show_bug.cgi?id=694874
Add Options dialog which allows users to set more options than current dialog.
The dialog reads printer's PPD file and add its options to the dialog together
with some preselected IPP options (#678637).
All operations in the dialog are asynchronous.
During implementation of this, the option for setting allowed users was removed
because this is not suitable for this panel (the option is intended for
administrators).
