Adds a watch link to the header to direct to the main twitch event page

Here's a pic of the header:
![watch_live_link](https://f.cloud.github.com/assets/711967/747304/9ede3cea-e456-11e2-94ea-9223fadfabe6.png)


Also, this is preferable (for molyjam at least) to embedding twitch livestreams on each venue page, because we're running an event hub on Twitch which will put all our users in the same chat channel no matter what stream they're watching.