Update grunt-react to use react-tools v0.12.0

Because React's update from 0.11 to 0.12 contains breaking changes,
grunt-react should update its version accordingly.
Tests have been updated to reflect update React functionality:
- `/** @jsx React.DOM **/` annotation no longer used
- js files will be transformed if valid React code is encountered

For reference, React 0.12.0 release notes are here: http://facebook.github.io/react/blog/2014/10/28/react-v0.12.html