Move to new repo to have a clean history

[felixmokross]

This repo has a lot of old commits and contributors from reveal.js itself. I would suggest to move it to a new one and archive this one.

While at it, we can also adapt the repo name to the course name, e.g. essential-react.

Maybe there is also a way to migrate PRs and the newer git history? But wouldn't bother too much with it, don't think its too important. The old repo would still be around, just archived.

For the exercise repo, we could also align the name with it then to make it easier to find.

We should also consider to move to the Zuehlke org -- not sure who has permissions to create repos there though.

[felixmokross]

Simple fix: just rename this repo (won't fix history issue, but already good enough)