Changes

• #494 Replaced reward options with command options. You can now execute commands when a player joins, leaves, wins, looses, ends in draw, scores a goal. Delete your arena_sample.yml to let it get recreated. The file includes examples at the line joinCommands.
• #494 This feature is also very useful to move players to certain permission groups during BlockBall games and remove them after the game. (e.g. only showing them a scoreboard if they are in a certain permission group)
• #494 Removed support for BungeeCord gamemode. These days bigger server use the server software Velocity and a dedicated gamemode is no longer neccessary. You can achieve the same thing with minigame mode.