Allow goggles to work on published thimble makes.

This is one has been nagging at me for a while, so I did some quick
testing and came up with a solution ;)

What this change does is essentially chage the bookmarklet code from:

```js

	(function () {
	    var script = document.createElement('script');
	    script.src = '-baseuri-/-lang-/webxray.js';
	    script.className = 'webxray';
	    script.setAttribute('data-lang', '-lang-');
	    script.setAttribute('data-baseuri', '-baseuri-/-lang-');
	    document.body.appendChild(script);
	})();

```

To this:

```js

	(function () {
	    var doc = document;
	    var urlParser = document.createElement('a');
	    urlParser.href = window.location.href;
	    if (/makes.org/.test(urlParser.host) && /^\/thimble\/(.*)[ ^ _]$/.test(urlParser.pathname)) {
	        doc = document.querySelector('iframe.embed-iframe').contentDocument;
	    }

	    var script = doc.createElement('script');
	    script.src = '-baseuri-/-lang-/webxray.js';
	    script.className = 'webxray';
	    script.setAttribute('data-lang', '-lang-');
	    script.setAttribute('data-baseuri', '-baseuri-/-lang-');
	    doc.body.appendChild(script);
	})();

```

*Where `-baseuri-` and `-lang-` get replaced on build.*

This sets the document to be either that of the make w/i the preview
iframe if on a published thimble project ELSE keeps it as the parent
page's document.

Bug: https://bugzilla.mozilla.org/show_bug.cgi?id=1026484
Test regex: http://bit.ly/1i7BQ34