Automate new version releases

[DimitarNestorov]

• Automatic PRs when a new version is released (whenever the version field in https://github.com/facebook/react/blob/master/packages/react-devtools-extensions/chrome/manifest.json changes)
• Automatic reports when README changes
• Automated tests
• Automated beta publish (when tests pass)
• Automated binaries
• Automated merge (when a % of reviewers accepts the PR)
• Automated publish (when the automatic PR gets merged)