Update to React 0.27

[winkerVSbecks]

[winkerVSbecks]

@r-bansal this is a bit more involved that simply updating package.json https://facebook.github.io/react-native/docs/upgrading.html

Also, just a reminder that we would have to update all the branches.

[relaxedtomato]

@winkerVSbecks Thanks, held off on making this update for now. Will bring it in after testing branches.