Sync to github

The arsnova.click v1 code is still available at github. We had a sync job in v1 and I think we need this for v2 again.

• Add a backend repo
• Add a frontend repo
• Add this repo to github as issue / documentation holder
• Add sync jobs for frontend and backend ci yml's (only staging and master)
• Add sync jobs for this repo (only master)
• Add notice to click v1 readme in github and gitlab that the code is deprected and link to the v2 repo