React: couple of improvements

Couple of improvements for Reactjs

1. Enabled calling a component factory with no arguments, eg ```MyComponent()``` (first argument was required in the defs, so you had to do ```MyComponent(null)``` if you didn't want to pass anything in)

2. Added a convenience overload to ```getDOMNode()```, with generic parameter of an element type, to cast the returned html element to a more specific type of ```Element```, eg ```HTMLInputElement```, ```HTMLAnchorElement``` etc.
Eg ``` this.refs['name'].getDOMNode<HTMLInputElement>().value```

Also an update in the tests for v0.12