Add networkAgent to initial-setup mode

We want to be able to set up e.g. a WEP connection on the
network page of gnome-initial-setup, so we need a network
agent in the session.

js/ui/sessionMode.js

@@ -81,7 +81,7 @@ const _modes = {
     'initial-setup': {
         hasWindows: true,
         isPrimary: true,
-        components: ['keyring'],
+        components: ['networkAgent', 'keyring'],
         panel: {
             left: [],
             center: ['dateMenu'],