add the ability to run from steam

Redefine the launch command in steam to `dayz-ctl %command%` and catch the launch state, exclude self-retraction

```bash
if [ "${2:-}" = SteamLaunch ] && [ "${3:-}" = "AppId=$DAYZ_GAME_ID" ]; then
  # xterm or https://github.com/i3/i3/blob/next/i3-sensible-terminal
  exec xterm -e dayz-ctl -T 'DayZ CTL Launcher'
fi
```