Generate classes from .idl files

DO NOT MERGE YET. I broke Karma and can't get it to come back to life due to subtle complications involving https://github.com/karma-runner/karma-traceur-preprocessor/pull/4 plus also RequireJS's horribleness as a packaging target. (I have an idea to fix it though...) Also I might want to figure out what to do with scripts/traceur-runner.js per the TODO left in there.

But anyway, this did shape up nicely.
Wish we had a style checker that worked on ES6 code.