Fix iframe reloading when moved

https://github.com/facebook/react/issues/858

My implementation allows components to be marked as `immovable` and `DOMChildrenOperations` then perform an strategy where it pre-moves `immovable` nodes into place before proceeding with the regular updates. If there are no `immovable` objects then this has virtually zero cost.

You can see it in action here:
http://dev.cetrez.com/jsx/2/

However, one major issue that needs to be resolved somehow for this to be functional would be to determine how the `immovable` flag should propagate up the hierarchy. This could be solved by propagating it up as an attribute on the nodes I reckon, but it may come at a slight cost as everyone would have to be checked in `DOMChildrenOperations` before moving on.