[future uncertain] Add support for pointer events

**The future of pointer events seem uncertain, this PR should not be accepted until it is decided.**

http://www.w3.org/TR/pointerevents/, only IE supports it at the moment it seems, you should be able to polyfill with http://handjs.codeplex.com/

1. I have reused EnterLeaveEventPlugin to power both Mouse and Pointer, feedback on my rewrite appreciated. One possibility is to construct a lookup map instead for isMouseEvent/isPointerEvent/isOverEvent/isOutEvent/etc, but I'm thinking it might just make the code more complex.
2. I took the liberty of stripping the alignment spacing in SimpleEventPlugin because I would still have had to realign everything, and this way makes future updates less likely to conflict. It's also consistent with ReactEventEmitter.
3. Should `mouseListenerNames` in `ReactDOMButton` include pointer events? Touch events too? Are there actually any events that you want it to attach when it's disabled?

```
   raw     gz Compared to master @ b75d11c6039e4d2ab796bce2a1934e9e69b2b7e7
 +4806   +613 build/react-with-addons.js
 +2175   +431 build/react-with-addons.min.js
 +4813   +591 build/react.js
 +2177   +446 build/react.min.js
```
Hello