React Native Web!

[bonham000]

This PR:

• React Native MVP!
• I added a basic React Native challenge with a simple test [1], and got it working in the Workspace and Torvalds. Getting the test to work correctly was a little difficult, I imagine testing these challenges may be a little harder than the others.
• The React Native challenges make use of a bundled version of react-native-web. We are building it with Webpack via this repo and copying the source file into the Workspace codebase. Any updates would require the file to be re-built.
• Fix loop-protect issue in production build closing #42.
• Refactor workspace to opt-in to running tests on initial load.
• Add default Workspace UI to cover the preview before tests are run [2].
• Fix a subtle bug preserving the lastActiveChallengeIds (discovered it from our tests 😎).
• Add a timeout on the Workspace test execution of 10 seconds which cancels the test run if the tests did not complete. If the timeout is reached the workspace test state will reset and the user will see a toast so they know the tests timed out.

Notes:

• I'm going to revisit the "mobile UI" preview in a later PR.
• Should we change the build settings and minify the react-native-web-lib.js file? I'm not sure.

Demo:

[1]: The React Native MVP Challenge:

[2]: The Workspace has an alternative default UI before the tests are first run:

[iansinnott]

What do you think about rewriting react-native-web to react-native in the user code the way codesandbox does?

[iansinnott]

* Should we change the build settings and minify the `react-native-web-lib.js` file? I'm not sure.

Hm, good question. How large is it? I'm thinking maybe we just leave it unminified if it provides better stack traces and the only visible downside is the loading time.

[bonham000]

I think we should go with renaming it to react-native, I think this is the general approach using react-native-web anyways. I'll update the code to reflect this.

Also, agree on using the un-minified version for (hopefully) better stack traces. This was also my same reasoning for including the development builds of React and ReactDOM. So I'll leave that the way it is now.

[bonham000]

@iansinnott just tagging you in case you want to review the replies I added above. I'll merge this in a bit later.

[iansinnott]

Awesome, thanks for putting this together