Check the actual whitelist for Player#isWhitelisted()

The server's check is for whether or not a player can pass the whitelist
not just if the player is on it. That seems like more useful information
but the API has always just checked if they are on it so this commit
restores that.
Check actual whitelist for CraftOfflinePlayer too
Use world-container when finding players to convert. Fixes BUKKIT-5530
Fix missed diff and other small things
Add methods to use arbitrary entries in scoreboards. Adds BUKKIT-3977
Added BlockTNT + EntityMinecartTNT for diff visibility.
Improved explosives.