[#70171542] Adds zendesk support tab to knowledge base pages.

*Requires https://github.com/AllPlayers/allplayers-mainline/pull/3692.
*Requires Zendesk support site to have it's domain changed to "support.allplayers.com".

![2014-04-30_0950](https://cloud.githubusercontent.com/assets/2251119/2843778/185c942c-d083-11e3-9c59-dee0f5754f13.png)
![2014-04-30_0951](https://cloud.githubusercontent.com/assets/2251119/2843779/1dfae2b2-d083-11e3-87ee-4ea5c9d7dc2d.png)