link and embed commbadge in app devhub (bug 907659)

Depends on https://github.com/mozilla/commbadge/pull/8

Created a small template and included commbadge's JS and some of its CSS. I created a ```section.commonplace-body``` element for Commbadge to use as its ```body``` and a ```div.commonplace-page``` to use as its ```#page```.

Added a link to developer hub sidebar.

Still need to iron out things such as what to do when no threads exist yet, updating Commbadge to jump from app version thread to app version thread.

Screenie
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![screen shot 2013-08-29 at 8 11 30 pm](https://f.cloud.github.com/assets/674727/1054993/e98cd2ea-1121-11e3-8940-c1e557ef718e.png)