Make a script that sets up worktrees for the git-* merge scripts

We could make a script that sets up the worktrees for git-pull-all, git-merge-forward and git-push-all.

For bonus points:

• Once we have a standard directory structure, we can put a sensible default config in those scripts.
• The script should clone tor, set up the remotes, and do a test git-pull-all.
• Refactor some common configs and functions out of the scripts.