KeepInventory Individual

Added command argument "list" (ki.admin.cmd.list) to get a list of players who have KeepInventory enabled.

Added command argument "help" (ki.admin.cmd.help) to get a list of commands for this plugin.

Added permission node "ki.keepxp" (default to op players) to prevent players from losing their experience levels upon death.

Various code optimizations were done for better plugin performance.