Add several spigot performance patches and update to latest upstream

Credit to appropriate authors is given in each patch file -- original author for each patch remains intact.
Always run Git to update submodules

Git won't redownload submodules if we have the last version, so there's
no point in adding an additional check.
Make OfflinePlayer Metadatable
Add a fix for servers deadlocking on startup
Update to the latest Bukkit/CraftBukkit
Merge remote-tracking branch 'upstream/master'