Add 'ready' command
Add health objective to all games
Keep track of game minutes

- Displays minutes in /ro command.
- New option time_updates to set update interval.
- match_minutes objective updates on all players.
Tidy ready message
Add killstreak objective
Add scoreboard death and respawn event objectives
Add match start and end objective events

- Refactor objective attributes for players, teams and game logic.
- Don't reset events on the scoreboard when match ends.
Add win and elimination event objs

- win_ev, team_win_ev, elim_ev, team_elim_ev, elim_status,
  team_elim_status.
- Fix onDisable scoreboard clear bug.
Fix event error when scoreboard changes
Fix no players added to game msg for team games
Remove support for adding players during game

Also remove support for players changing teams during the game. These
are minor features, and require a lot of handling for each game,
so time best spent elsewhere.
Move scoreboard command to setscoreboard

- Move '/ro scoreboard main' to '/ro setscoreboard use_main',
  to allow for other scoreboard options to be added.
- Refactor listing game options.
Fix match start being allowed during countdown
Fix elimination ranking
'player add chan' will only work on online players
Remove chan members when they go offline

- If not playing a game, offline players are removed from their
  channel.
- All handling of channel members works better for the user, the
  intuitive behaviour is that offline players are not affected by
  commands.
- rf_data remembers the previous channel, and if it still exists, the
  player is put back there on server rejoin.
- Also, stop cancelling game runnables every time a player is deleted
  from the channel dictionary.
Fix 'chan join' undefined var
Fix not being able to switch main scoreboard off
Fix game minutes not resetting at end of game
Fix non-player kills assistance player KeyError