Use firebase for live-writing

this was *not* as easy as I first thought! 

Here's a rough semi-working version. We simplify the reader side of things by just binding to a firebase collection. Now, at the writer side of things it gets a bit more complex. We have to basically keep a firebase collection in sync with what's being written (doing it server-side would be too costly and sort of defeat the point I think?) 

It doesn't fully work, I just wanted to check your thoughts, it seems a little bit hacky. 

IF we were only using firebase, and we had a little ember app as the writer, this would be so simple. You just call the usual ember.set commands and it all happens automatically. But we aren't :P