Revert "network-manager-applet: do not use appindicator because it breaks the menu"

This reverts commit 3008aff7be24c01336401d1c83089d8c840017b4.

Do use the appindicator so that we get the nicer interface
behaviour, and nm-applet to lightdm/unity-greeter login screen.
indicator-applet is patched so that the disappearing menu bug
should not exist.