Update to React >= 15.5.4

[islemaster]

Next step along the road to React 15.6.1, following on #16856.

Changes in this minor version that we had to address:

• react-addons-test-utils goes away, replaced by react-dom/test-utils.
• React.PropTypes is deprecated in favor of the separate prop-types package.
• React.createClass is deprecated in favor of create-react-class (or preferably, ES6 classes)
• Also update dependencies that might be using these.

[islemaster]

Closing (this is very out-of-date now) and trying to do more incremental cleanup.

[pcardune]

👏