Validate Server method input. Addresses BUKKIT-3687

CraftServer methods that implement the Server interface will throw an
IllegalArgumentException if a method cannot operate on a null input
and given a null pointer.

This causes methods to fail early and identify that a plugin is
responsible for passing in an invalid argument. This will only
change the exception thrown, if there originally was a thrown
exception. This helps with hunting down legitimate problems
with CraftBukkit.
POM Changes.
Spigot changes.
Address BUKKIT-3286 by firing the inventory close event when a secondary container is closed due to the player entity being destroyed. This covers all edge cases such as server stop / player kick / player quit.
Update item merge logic
Include NibbleArray from mc-dev for diff visibility
Implement 'lightening' of NibbleArrays - only allocate buffers when non-trivial value Saving from 40-45% of memory use by chunk section data.

Finish up NibbleArray lightening work - use for Snapshots, reduce copies

Fix nibble handling with NBT - arrays aren't copied by NBTByteArray
Return LOHS to full operation.
Per world view distance.
Fix various crop growth modifier formula issues
Add OldChunkLoader from mc-dev for diff visibility
Fix mcRegion-to-Anvil conversion
Update versioning check to correctly resolve api version.
Optimize packet used to unload chunks for the client

At the moment telling a client to unload a chunk involves calling the entire chunk from memory, deflating it and then sending it through the pipes even though the client ignores it and based on the bitmap simply unloads the chunk, and to add the cherry on top, this is done on the main server thread.
Skip entity.move() if we are not moving anywhere.
Alternate, sync-free-but-safe chunk reference cache
Tick loop optimization - sleep for as long as possible.
Improved Timings System

Tracks nearly every point of minecraft internals and plugin events to give a good quick overview on what is causing TPS loss.
Better + more flexible itemstack merging
Add oreobfuscator for Spigot.