Status area: add NetworkManager indicator

Adds an implementation of nm-applet in javascript. Uses the new
introspection from NetworkManager, and temporarily requires
nm-applet to be running for the secret service.
Features a renewed interface, with each device controllable through
a switch, which if toggled off disconnects, and if toggled on
connects to the most recently used valid connection. More esoteric
features like creation of ad-hoc networks have been moved to the
control center panel.

https://bugzilla.gnome.org/show_bug.cgi?id=621707

js/ui/panel.js

@@ -44,6 +44,12 @@ const STANDARD_TRAY_ICON_SHELL_IMPLEMENTATION = {
 if (Config.HAVE_BLUETOOTH)
     STANDARD_TRAY_ICON_SHELL_IMPLEMENTATION['bluetooth'] = imports.ui.status.bluetooth.Indicator;
 
+try {
+    STANDARD_TRAY_ICON_SHELL_IMPLEMENTATION['network'] = imports.ui.status.network.NMApplet;
+} catch(e) {
+    log('NMApplet is not supported. It is possible that your NetworkManager version is too old');
+}
+
 // To make sure the panel corners blend nicely with the panel,
 // we draw background and borders the same way, e.g. drawing
 // them as filled shapes from the outside inwards instead of