Multiarena Duels [1v1]

New Features:

- Added bStats Metrics. This can be disabled in the bStats folder (\plugins\bstats)

- Added the ability to challenge other players to a duel by doing /duel challenge <player>. This can be accepted by doing /duel accept.

- Added kits. /duel createkit <name> creates a kit with your current inventory. /duel kits lists all kits. /duel kit <kit> equips a kit. /duel deletekit <kit> deletes a kit.

- Duels tracks your win count and keeps a leaderboard. The top ten can be seen by doing /duels top.

Bug Fixes:

- Players are not stuck in adventure mode after their duel.

- [Duels] is colored correctly in all of its messages and its colors are configurable.

- Disconnecting in a duel now results in a loss.