Minor commit to make addon work with CTR.

Since Australis the App Button has been removed (ugh) and so an add-on called Classic Theme Restorer tries to revert this change but adding another button with the ID "ctr_appbutton".

This is a minor commit that looks for the "ctr_appbutton" if the real button isn't existing thus making the add-on work with CTR.

Add-on Location: https://addons.mozilla.org/en-US/firefox/addon/classicthemerestorer/