Adding code quality measurement via CodeClimate

I've been trying out this new code quality measurement service called Code Climate on some of my code and I think this project could benefit from it.

Basically it's like running JSHint/JSLint on the project, except that tests are ran online and results are available on their website. Which means easy to setup, easy to have feedback.

I tried it on my fork of the project (here: https://codeclimate.com/github/ThibWeb/Iframe-Height-Jquery-Plugin/issues) and it reported a lot of "issues". Some real, some easy to fix, many not that important. There's no need to fix them all, but it is always good to have some QA.

Anyway, it is free of charge and really easy to setup for OSS projects if you want to have a look: https://codeclimate.com/github/signup.