Add enhancments to brewing. Adds BUKKIT-2441

Split from GlowstoneMC/Glowkit#3
Original Bukkit PR: Bukkit/Bukkit#1070
Additional changes: None
Glowstone implementation: Not done

-----

Previously it was not possible to determine when brewing has ended or what
potions were involved in a brew event. These are required for plugins to
fully deal with brewing in Bukkit.

This commit adds the capability to have that support.