Add compatibility with React 15.5.0 and onwards

[rake5k]

• From https://www.npmjs.com/package/react-addons-css-transition-group:

  The code in this package has moved. We recommend you to use CSSTransitionGroup from react-transition-group instead.

  In particular, its version 1.x is a drop-in replacement for the last released version of react-addons-css-transition-group.
  Run npm install --save react-transition-group@1.x, and replace the imports in your code:

  // Old 
  import CSSTransitionGroup from 'react-addons-css-transition-group';
   
  // New 
  import CSSTransitionGroup from 'react-transition-group/CSSTransitionGroup';

• From https://www.npmjs.com/package/react-addons-test-utils:

  This package is deprecated as of version 15.5.0:

  • TestUtils have been moved to react-dom/test-utils
  • Shallow renderer has been moved to react-test-renderer/shallow

[miraage]

@dcurletti could you please take a glance on this issue? It's also implemented #42