createClass is depreciated

[erasmuswill]

In #229 it was mentioned that the examples were updated for React 16. However, all of the examples still recommend using
var base = Rebase.createClass(app.database());
createClass has been deprecated:

content.bundle.js:22791 Warning: Accessing createClass via the main React package is deprecated, and will be removed in React v16.0. Use a plain JavaScript class instead. If you're not yet ready to migrate, create-react-class v15.* is available on npm as a temporary, drop-in replacement. For more info see https://fb.me/react-create-class