Add support for the main server scoreboard

- '/ro scoreboard main on' enables the main scoreboard on any channel.
- '/ro scoreboarrd main off' disables.
- Adds new robofish.main_scoreboard permission.
- Replaces deathmatch 'score_mode' with 'losses' option.
- Changes how deathmatch scores are tracked. Points are not synced to
  kills and losses. Kills give +1 to points, losses give -1 if enabled.
  They are otherwise separate.
- Updates all scoreboard objectives with more descriptive names, as they
  are now user-facing.
Add '/testfor' scoreboard hook for match status

The objective has to be set on all game players, because you can't
/testfor any offline players.
Copy team scores to players to support /testfor
Only sync scoreboard updates if using main sb
Update README
Support adding eliminated players back into game

This is necessary for fully support player points as a writeable
scoreboard objective.
Add setscore command to edit game scores

This is a cleaner alternative to letting users control game scores via
the /scoreboard command. It can still be triggered by command blocks,
but gives us more control over what objectives can be edited, and it
gives the user a simpler interface.

Also adds robofish.change_scores permission.
Remove read and write prefixes from objectives

These aren't necessary, it's better to not drop the scoreboard command
in favour of /ro setscore, and to give tidier objectives to /testfor.
Add help and tab completion for /ro setscore
Support 'me' and 'chan' shortcuts in setscore

And fix setscore tab completion.
Replace change_scores permission with all admins
Cleaner rejection of command blocks and console
0.1.8