React 0.12

[chulkilee]

• Replace ReactDescriptor with ReactElement (fix React v0.12 Errors: react/lib/ReactDescriptor not found #433)
• Replace removed mixInto with Object.assign - using object-assign polyfill
• Other deprecated methods are not replaced (e.g. merge, copyProperties etc). probably better to fix them together.

Note that react uses own polyfill for Object.assign - see facebook/react#1998 and facebook/react#2350

Also this will not work on react < 0.12. I think previous versions should have depend on ^0.11.0, not >= 0.11.0.

[gaearon]

I think it would be better to use .prototype as in #434 instead of adding a polyfill dep.

[ryanflorence]

Thanks! closed by 70b442a