Bug #10751.1: Load HUDService only if it's not already available.

Loading by this method breaks the browser console in ESR31.
Fortunately, ESR31 has a built-in window.HUDService.
Bug #10751.2: Adapt Torbutton to Australis UI.

Use CustomizableUI, if it is available, to add TorButton's
button to navigation toolbar.