Fix teleport failing right after join. Fixes BUKKIT-5479

Teleporting a player checks to see if the player is disconnected to
try to avoid creating ghost players. The check it uses, however, randomly
fails when the player is in the middle of joining the server. The check
that would work correctly here does not work correctly when the player
actually disconnects. To work around this we add a new flag which is
cleared on the first tick of the new player and assume they are connected
if the flag is set.
Fix missed diff making horses lose their saddle
POM Changes
mc-dev imports
Skeleton API Implementations
Spigot Configuration
Better Chunk Tick Selection
Crop Growth Rates
More Efficient Chunk Save Queue
Merge tweaks and configuration

This allows the merging of Experience orbs, as well as the configuration of the merge radius of items. Additionally it refactors the merge algorithm to be a better experience for players.
LongHash Tweaks
Async Operation Catching

Catch and throw an exception when a potentially unsafe operation occurs on a thread other than the main server thread.
View Distance

This commit allows the user to select per world view distances, and view distances below 3. Be wary of the issues selecting a view distance of 1 or 2 may cause!
Compressed Nibble Arrays

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
Sync Free Chunk Reference Cache
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.
Fix Mob Spawning Relative to View Distance
Handle Null Tile Entities
Entity Activation Range

This feature gives 3 new configurable ranges that if an entity of the matching type is outside of this radius of any player, will tick at 5% of its normal rate.

This will drastically cut down on tick timings for entities that are not in range of a user to actually be "used".
This change can have dramatic impact on gameplay if configured too low. Balance according to your servers desired gameplay.
Metrics