Added support for Spigot #1521 by countering its NBT scrubbing.

After build #1521, Spigot automatically scrubs every outgoing item
stack of custom NBTs. This breaks ItemRenamer as it uses a custom 
NBT to store the original item stack.

We work around this by adding a packet output handler that will
undo this scrubbing. 

See this thread for more details:
www.spigotmc.org/threads/spigot-build-1521-corrupts-nbt-data.22682/
Increment to 2.2.3-SNAPSHOT