Wip social feed refactor

@crissmancd , This is the start of refactoring the social feed widget so we can add Facebook and Google+. Since you created the original animal, I figure you're the guy to give a little input on this. There's still a lot to do, so I'm hoping for some thoughts on the general direction this is headed rather than a micro-analysis of the details.

There are very few changes to the logic. Mostly I've just reorganized some code. The one significant modification here is that almost all the widget markup is now generated by the Javascript. That lets us spray a navigation tab and a content block into the DOM only for those feeds that contain valid options. This way, we can choose to display any combination of one or more of the feeds. The previous code sort of did that with conditionals in the HTML, but moving it into the JS gives us a bit more power. 

There's still a lot to do here with timing of events, validation of params, and code cleanup, but the base logic is what I'm planning to roll with when I add in the other two feeds. 

So, any thoughts on this before I forge ahead?