feat(index): turn throw 'expect called with WebElement' into console.warn

Throwing the error might be useful to avoid newbies problems but I'm trying to use a Jasmine 1.3.x [custom](https://gist.github.com/elgalu/94284ec0ac3e8a590507) matcher `toHaveClass` that is able to work on ElementFinders and WebElements, usage looks like:

```js
expect(elmFinder).toHaveClass('ng-invalid');
expect(webElm).not.toHaveClass('ZZZ');
```

Only way to get it working is with this PR