Combine dev servers into a single url for easy development

[Greenheart]

To simplify development and not have to type the full URL like http://192.168.0.64:3000/play?path=http://192.168.0.64:5000/default.json on mobile devices, we could combine the dev servers into a single one.

I will look into building scenarios into the web/static/dev-only directory during development to allow them to be accessible from the same static server. This will allow us simplify the project config for development and remove some dependencies, making the project lighter to run in dev mode.

This should not affect how scenarios are built for production, as they should still be built into content/dist to be able to be deployed separately.

TODO:

• [x] During development, build scenarios to web/static/dev-only instead of content/dist
• [x] Ensure web/static/dev-only is added to .gitignore
• [x] Ensure web/static/dev-only is removed before the built app gets built and published
• [x] Ensure production builds of scenarios are still built to content/dist
• [x] Remove unnecessary dependencies
• [x] Simplify dev scripts
• [x] Update README.md and CONTRIBUTING.md with new instructions.
• [x] Add ?dev=[SCENARIO_ID] path parsing support to the game client, to automatically load development scenarios. Will greatly improve local development experience.

[Greenheart]

Resolved with https://github.com/Greenheart/swipeforfuture.com/commit/6e004424a36cd5a9a1cc6fe92d662f0c527b5754 and related previous commits! 🎉