wizard-window: API to show file chooser widget

Add a view and API to show file chooser to user.

https://bugzilla.gnome.org/show_bug.cgi?id=741046
wizard-toolbar: Content for file chooser view

The wizard topbar should provide a different set of controls and title
when file chooser view is visible in the properties window.

https://bugzilla.gnome.org/show_bug.cgi?id=741046
wizard-source: Drop use of file chooser dialog

Instead of creating and launching a separate dialog to let user select
ISO960 files/devices, use the new WizardWindow API to present an in-view
file chooser.

Nested dialogs is something we want to avoid according to our designers.

https://bugzilla.gnome.org/show_bug.cgi?id=741046
wizard-window: Request size 1024x768

The wizard window is currently very small and it looks ugly,
especially now with FileChooser view in it. Lets give it a decent size.

https://bugzilla.gnome.org/show_bug.cgi?id=741046