[B+C] Send QuitReason when the PlayerQuitEvent or PlayerKickEvent is fired. Fixes BUKKIT-429

Adds feature requested in BUKKIT-429. https://bukkit.atlassian.net/browse/BUKKIT-429
Bukkit PR: Bukkit/Bukkit#726

This change causes the CraftBukkit server to report the reason for a player's disconnection to the PlayerQuitEvent. See the Bukkit PR for more details.

### Status
 - [ ] Waiting for author (@dualspiral)
 - [ ] Waiting for PRH (@riking)
 - [x] Waiting for core