dillon1000/react

Move key/ref off props and prepare for new descriptor factories

Breaking changes

- key/ref are no longer accessible on props but they are accessible on the
  descriptors. This means that parents/owners can access it but not the
  component itself.

- Descriptor factories are now plain functions and you can't rely on the
  prototype or constructors of descriptors to identify the component type.

Existing descriptor factories are now wrapped in a legacy factory. Currently it
does nothing but it will give us a hook to track callers to factories that are
not using JSX but just invoking the function directly. It also proxies static
methods/properties to the underlying class. The newer factories don't have this
feature.

ReactTextComponent has it's own little factory because it's props is not an
object. This is a detail and will go away once ReactTextComponent no longer
needs descriptors.