Pages published via gh-pages branch + separate scrape workflow

[sverhoeven]

Fixes #1

TODO

• after merge in repo settings switch GH pages source to gh-pages branch.

Pros:

• by running scrape workflow only index.json is updated

Cons:

• uses old way for deployment, current is to use https://github.com/actions/deploy-pages action
• with each run of workflows the repo gets a new commit, growing the repo by ~500Kb each time.