Tracking issue for improving launchd support

[Enzime]

• Make sure all nix-darwin managed units are loaded in
• Back up existing files before replacing them
• Restore backed up files when uninstalling nix-darwin
• Replace usage of {un,}load and boot{out,strap}
• Use more descriptive names than sh for Login Items in System Settings

[Samasaur1]

Should this also include the work that needs to be done to have them show with nicer names in System Settings, or should that be its own tracking issue?

[Enzime]

Updated 👍