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

data/theme/gnome-shell.css

@@ -153,6 +153,14 @@ StTooltip StLabel {
     spacing: .5em;
 }
 
+.popup-inactive-menu-item {
+    font-style: italic;
+}
+
+.popup-subtitle-menu-item {
+    font-weight: bold;
+}
+
 .popup-menu-icon {
     icon-size: 1.14em;
 }