Optional parameter to list-classes command

Usage: !list-classes heavy medic scout

If classes are provided as the optional parameter, it will only list the players added for those particular classes.

If the player is not an admin, and doesn't provide an argument - the command won't work.

If the player is not an admin, it truncates to just the first valid class they entered

Admins can do as many classes as they want, or not use an argument to show the full list

It should work, but this code is untested.... sorry.