[Bleeding] Fix Achievement and Statistic API. Fixes BUKKIT-5305
[Bleeding] Add /achievement command. Addresses BUKKIT-4932
Add ServerListPingEvent player list API. Adds BUKKIT-5121, BUKKIT-2465
[Bleeding] Fix logic for calculating slot in Creative mode. Fixes BUKKIT-4715

Previously, hotbar slots for player inventory would return 9 - 18 while in
Creative mode, rather than 0 - 9. This commit fixes the logic used for
calculating the returned slot based on the raw slot.