Re-factor setupComponent to set this.$node as passed element/HTML

Currently the documentation is incorrect. This does not pass:

```javascript
setupComponent('<span class="foo">Test</span>');
expect(this.component.$node).toHaveClass('foo');
```
This is because `this.$node` is set to `$('<div class="component-root" />');` instead of the passed HTML.

I realise this can be worked around (as it is in the test examples) by using `this.$node.find('.foo')` but this doesn't feel very clean.

The reason for my changes are that I actually need to the `this.$node` property to be my element. Example:

In my component:
```javascript
this.$node.append(someHTML);
```

I'm expecting:
```html
<div class="my-components-node">
    <div>someHTML</div>
</div>
```

What happens in test:
```html
<div class="component-root">
    <div class="my-components-node"></div>
    <div>someHTML</div>
</div>
```
Also making use of the API for adding fixtures via [jasmine-jquery](https://github.com/velesin/jasmine-jquery)

Thanks