provide better start scripts for Unix

The bundled start script start_crowd.sh runs Crowd in the foreground. While this is fine for testing, production systems will usually want it to run as a daemon, by running "catalina.sh start" instead of "catalina.sh run". Of course, it's trivial to change the script, but it would be nice if it came like that by default.

Also, it would be nice to provide a stop script with the distribution.