Add exclusive content message to developer pages (bug 946001)

https://bugzilla.mozilla.org/show_bug.cgi?id=946001

**Screenshots:**
![screen shot 2013-12-03 at 17 00 04](https://f.cloud.github.com/assets/187006/1715520/3a0b7fb8-61b4-11e3-84b2-0055fa918686.png)
![screen shot 2013-12-03 at 16 55 24](https://f.cloud.github.com/assets/187006/1715521/3a113de0-61b4-11e3-8550-1f107cc1b846.png)