Add jscs package and basic conf.

Add [node-jscs](https://github.com/mdevils/node-jscs) package and a basic configuration based on existing [code conventions](https://github.com/MattiSG/Watai/wiki/Code-conventions). 
This configuration needs to be enhanced.

To check the code:

```js
$ npm run lint
```

There are many "Var declarations" errors (multiple `var`). Should be fixed.
As mentioned in the [code conventions](https://github.com/MattiSG/Watai/wiki/Code-conventions#code-style), Watai's base is Google's style guide. Is there any reason for not using `jscs`’ associated [preset](https://github.com/mdevils/node-jscs/blob/master/presets/google.json)?