Add persistence

[yesezra]

A deployment should store:

• defaults per screen
• authentication credentials

[mick]

I think redis would be a good options for this. I'd like to add it soon, because the screen default isnt really useful until we have this (since heroku idles the service)

[yesezra]

Yeah, Redis sounds good to me.

[mick]

I'd like it to check for redis and fail a bit more gracefully (it wont die now, but it will complain to log a lot)

[mick]

So it backs off nicely right now. That's good enough. If there are any issues with that we can set a config to disable redis persistence as a feature.