eggimagemenubutton: Copy and un-deprecate GtkImageMenuitem

This was deprecated without reference to a bug or reasoning,
and we need it for our importer drop down button. We want
to show the device image in the drop down menu. So copy it
from GTK+, clean it up, and keep using it.

Add a tool to test GcrImportButton
gcr-comparable: Fix documentation warning
ui: Stop using GtkStock now that it's been deprecated
gcr-display-view: gtk_icon_size_lookup_for_settings() deprecated

Use alternative
gcr-unlock-options-widget: gtk_widget_get_state() deprecated

Use alternative
gcr-importer: Debugging and doc tweaks