Switch from Classic Theme Restorer add-on to Firefox notification box

This PR replaces/removes the Classic Theme Restorer extension, which allowed us to use the Add-on bar which was removed in Firefox 29, with basically the same functionality being provided by Firefox's "notification box". Hat tip @miohtama for pointing out this possibility, thanks! See https://developer.mozilla.org/en-US/docs/Mozilla/Tech/XUL/notificationbox for some basic info.

As of now it still needs improvement, in particular: the icon on the bar needs to be better. Also I'm noticing a javascript error that comes up in the console for each audited page (doesn't affect functionality but want to know what it is/remove it). A bit more tidying up in script.js may also be helpful.

Worth emphasising that even if there is some slight disadvantage, it is highly desirable to remove the dependence on CTR (which we simply bundled in as a stopgap). So far I don't see a meaningful disadvantage (another advantage I note is that in the old version, the user closing the addonbar would simply stop the buttons being available for the rest of the audit I believe, whereas here the next notification bar will still come up if the previous one was closed).

This PR is not yet ready to merge, as it hasn't been tested sufficiently, but I put it here so that others can try it and report feedback. Thanks.