Feature request for ticket #6, scoreboard command.

This command is not fully implemented yet.

Proposed command syntax examples:
'/sb' = 'sb' stands for Scoreboard.

* Increment | increase by one.
/sb inc {arena} {player}

* Adds specified amount to the players score:
/sb add {arena} {player} {amount}

* Undo the last scoreboard command:
/sb undo
Merge branch 'master' of https://github.com/BattlePluginsDev/BattleArena