improve configurability and make redis optional

[wenzowski]

This is a quick proof of concept that depends on unreleased code, but could be merged following release of next Derby & Racer alphas if the addition of convict doesn't bother anyone.

The tarballs in package.json are currently tags of derby & racer master. They're there because c9.io can't resolve git locations right now.

Environment defaults proposed do not represent strong opinions, but just examples.

[wenzowski]

Note to self: c9.io is a giant pain in the ass. Just use Codio.

[wenzowski]

Also, this pull doesn't completely remove redis until @josephg finishes extracting the RedisDriver from livedb

[wenzowski]

Working with all examples as of derbyjs/derby-examples#44.

Would be great if @nateps or whoever is currently deploying the examples repo could chime in on whether the hosted demos should continue to use redis. If yes, I can resurrect the $REDIS_ENABLED toggle and remove pinned sha1s, and this is good for merge (if you don't think the mozilla config too adds too much extra weight–it's only ~400 lines).