Per-command argument restrictions and small fixes

- Can set argument restrictions for string and number arguments only.
- String arguments should be either a single string, or an array of
strings that the rank can use in the command.
- Number arguments should be a table with a "Min" and/or "Max" entry
that restricts the range of the argument.
- User data format is a table entry instead of a string entry in the
"Commands" list for the rank.
- Fixed pregame "waiting for players to load" message persisting after
the plugin is unloaded.
- Fixed unloading the tournamentmode plugin causing error spam and not
preserving previous auto-balance settings.