Upgrade react and dependencies to v16.4.2

[apburnes]

Upgrade React to newest version to support new Draftail features.

• Resolves Upgrade to latest version of React v16.x #2291 and resolves Add polyfills to React 16 update to support IE customers #2330

Impacted areas of the application

• The Wagtail Draftail editor
• The https://www.fec.gov/legal-resources/ search, filter, and display functionality
• JS tests of draftail and legal react components

To Do

• Upgrade react, react-dom, and any other dependencies
• Upgrade enzyme and karma JS testing dependencies
• Check functionality on the Wagtail Draftail Editor and functionality of https://www.fec.gov/legal-resources/

[patphongs]

This PR is contingent on testing for React on feature: #2307. This testing will be completed on 9/6.

[patphongs]

@apburnes This is looking good, testing has been completed for React 16. The only extra thing that needs to be added to this PR is the polyfil for IE that you implemented on the feature branch PR: #2298

[patphongs]

Changes look good, thanks!

[johnnyporkchops]

Tested locally in a few page types and draftail editor works as expected. I am getting a console error that seems to occur locally whenever ../package-lock.json is changed in a branch--so I don't think its related to any of the React upgrades here, but just flagging in case. If no one deems this an issue, I can approve and merge.