gnome-keyring [RFC] PKCS#11 certificate chooser

[Lubomir Rintel <lkundrak v3 sk>]

Hello,

We'd like use PKCS#11 URIs with NetworkManager VPN plugins and WPA-TLS.
I'm following up with a prototype of the choser button and related widgets.

I'm aware that Prashant did some work on this, but the activity seems to have 
ceased and the work that was done seemed not match the expected UI wireframe 
from bug #679860 [1]. Therefore I chose to start from scratch following the 
GtkFileChooser* instead. That might or might not have been a good idea;
either way -- I'd be glad if manage to somehow get a working certificate picker.

[1] https://bugzilla.gnome.org/show_bug.cgi?id=679860

I'd be very thankful if someone with a better understanding of PKCS#11 tokens 
and Gtk than I have could take a look.

Thank you,
Lubo