Adds React static methods (Component.Method)

This will add support for doing React static methods, as per #22. 
The solution might not be pretty, but opening this pull request to have an open discussion.

Now you can do something like (from tests):

```js
var mixins = [{ statics: { foo: noop } }, { statics: { bar: noop } }];

var Component = component(mixins, function () {
  return React.DOM.text(null, 'hello');
});

Component.foo.should.be.a('function');
Component.jsx.foo.should.be.a('function');
Component.bar.should.be.a('function');
Component.jsx.bar.should.be.a('function');
```