Use Classes in the React Template

[ntwcklng]

To match the Preact & Inferno Template, we should use Class x extends React.Component for creating a React Component instead of React.createClass({}).
In the near future React.createClass({}) will be replaced with Class x extends React.Component. See https://facebook.github.io/react/blog/2015/03/10/react-v0.13.html

[insin]

I think we should do this when/if we drop the react-transform Babel plugin in favour of the latest React Hot Loader, which AFAIK supports patching methods defined as class properties for binding.