Provide Code-Sandbox templates for more complete playground environments

[ryyppy]

The playground is quite limited with its runtime capabilities, due to some complexities.

Here are a few details what the playground should be:

• A tool to quickly show-case the JS output for a ReScript program
• A quick way to try out new compiler features
• A way to report certain bugs for specific compiler releases
• (future) An exploratory tool for showing the AST?

Runtime wise, it would be best-case if we are able to console log stuff, but we don't really want to be able to render whole React programs.

To help users to try out ReScript in a more desktop like experience, we should find a way to provide a Code Sandbox template (maybe as a link on the playground page?), so that users can actually build whole ReScript apps in the browser.