Add JSCS for consistent style

This PR adds [JSCS](https://github.com/mdevils/node-jscs) as a dependency to help us keep consistent style. I've updated all the JavaScript files (except the Rhino tests and packaged versions) to get us off to a good start.

I've set the "Crockford" preset in the `.jscsrc`, as it mostly matches the existing code (@cjohansen previously used JSLint to keep the code lint free). It's been adjusted with a few settings.

In the `test/ci-test.sh` we will verify the style before running unit tests.

##### TODO

- [x] Figure out how to get rid of the `_stack` in `lib/sinon/util/core.js`, so we can enable `disallowDanglingUnderscores` again

---

If this gets merged, I'll add a pre-commit hook that people can install as part of bootstrapping their development setup. That should cut down on the frustration of having a style checker run on CI, as you get immediate feedback.