content rating detail link in ratings section (bug 945936)

[Mock](https://bug929805.bugzilla.mozilla.org/attachment.cgi?id=822465)

![screen shot 2013-12-03 at 2 41 42 pm](https://f.cloud.github.com/assets/674727/1668842/e815f9f0-5c6c-11e3-9b6b-02f520a7512d.png)

![screen shot 2013-12-03 at 2 42 43 pm](https://f.cloud.github.com/assets/674727/1668844/e929c98e-5c6c-11e3-8be4-33122b3a20d6.png)

TODO: make content ratings section prettier (smaller icons, ```clear``` the description on mobile).