Move from "master" to "main" as default branch across all projects

Why?

https://www.theserverside.com/feature/Why-GitHub-renamed-its-master-branch-to-main

Steps required:

https://www.r-bloggers.com/2020/07/5-steps-to-change-github-default-branch-from-master-to-main/

Additional changes

Also update the WebHook settings in all repositories, to only listen on push events on the main branch, instead of master branch (except "Player", which is on main already).

Projects

• Meta
• Steering
• Dashboard
• Dashboard Clock
• Tank
• Engine
• Engine Core
• Engine API
• Engine Recorder
• Player