change current .first() behavior to return a query object and add .raw() for raw nodes.

It's becoming increasingly common to want to continue chaining passed `.first()` now that there is a `.statements()` method, e.g.

```
$functionExpression.statements().first().prepend('debugger');
```

This may be important for .map, .filter, et al too. It starts to be unclear when a query object turns into an Array during chains.
