Add JSON-Schema

[listefano]

This PR adds JSON-Schemas for the following files. This could be used for a future CLI editor or web based editor to validate the input.

Also if someone edits the .json files with an editor that understands JSON-Schema like vscode. You get features like auto completions and inline documentation.

[EddyVinck]

Hi @stefanrempe! Thanks for your contribution!

If you'd like make additional contributions and would like an easy way to communicate with other contributors and myself you can join our community Slack. We also have a :love_letter: newsletter if you're interested 🙂

I will take a look at the PR after work. Also, we're already working on a CLI here: https://github.com/EddyVinck/ConfTalks/pull/12. You can join the discussion here: https://github.com/EddyVinck/ConfTalks/issues/11

[jglover]

@EddyVinck in my opinion this would be worth merging regardless of any CLI tooling etc. JSON schema definitions are considered best practice and this will have no impact on any other on-going work but provides some benefits. I'd really like to see this merged