Include defaultProps of component in props passed to connect callback

Hey,

I'd like to be able to specify defaultProps on a Component decorated with `connect`, and to have those added to the props passed to its callback:

```js
class Foo extends React.Component {}
Foo.defaultProps = {
bar: 'baz'
}

connect(props => ({
fetch: `https://some.thing/${props.bar}`
}))
```

I'd be up for implementing this if there are no objections.