Breakout `react` package

[matt-landers]

This issue is in response to @wjohnsto's comment on #194

In order to create a clear delineation of dependencies, a react package should be created with react specific features. Do not mix Next features in the react package. This package should include (but not limited to):

• Hooks for data fetching (usePost, usePosts, etc.)
• Gutenberg block processing for react components
• Mechanism for registering components with the framework
  • Provide data requirements

[blakewilson]

I have a working branch for this package here: https://github.com/wpengine/headless-framework/tree/feat-react