upgrade React dependency to React 0.12

cf http://facebook.github.io/react/blog/2014/10/28/react-v0.12.html

1/ renderComponent* becomes render*
2/ React.DOM.* should no longer be used. According to http://facebook.github.io/react/blog/2014/10/16/react-v0.12-rc1.html, "All JSX tags that start with a lower-case letter or contain a dash are treated as HTML"
3/ a component can no longer be used as a function. It needs React.createElement - https://gist.github.com/sebmarkbage/ae327f2eda03bf165261

All tests are passing. I had to modify the mock ; the modification took the "fast" way as I decided to leave the React.DOM mock at this stage.