Only send maps in item frames upon tracking

Maps in item frames are full of bugs.
1) It sends an update of the Maps data to ALL players in the world, not just the players tracking it.
2) It sends an update EVERY tick, not every 10 ticks as intended.

To optimize performance of maps in item frames, we will only send it once a player tracks the ItemFrame until it completes, then that player will not receive more updates.

This means cursors will not dynamically update, but the map data should refresh every time the player moves away then back.
Detect, remove and warn about null tile entities.
Tick loop optimization - sleep for as long as possible.
Netty

 Implement an uber efficient network engine based on the
 Java NIO framework Netty. This is basically a complete rewrite of the
 Minecraft network engine with many distinct advantages. First and foremost,
 there will no longer be the horrid, and redundant case of 2, or even at
 times, 3 threads per a connection. Instead low level select/epoll based NIO
 is used. The number of threads used for network reading and writing will
 scale automatically to the number of cores for use on your server. In most
 cases this will be around 8 threads for a 4 core server, much better than the
 up to 1000 threads that could be in use at one time with the old engine. To
 facilitate asynchronous packet sending or receiving (currently only chat), a
 thread pool of 16 threads is kept handy. == Plugin incompatibilities As a
 side effect of this change, plugins which rely on very specific
 implementation level details within Minecraft are broken. At this point in
 time, TagAPI and ProtocolLib are affected. If you are a user of ProtocolLib
 you are advised to update to the latest build, where full support is enabled.
 If you are a user of TagAPI, support has not yet been added, so you will need
 to install the updated ProtocolLib so that TagAPI may use its functions. ==
 Stability The code within this commit has been very lightly tested in
 production (300 players for approximately 24 hours), however it is not
 guaranteed to be free from all bugs. If you experence weird connection
 behaviour, reporting the bug and steps to reproduce are advised. You are also
 free to downgrade to the latest recommend build, which is guaranteed to be
 stable. == Summary This commit provides a reduction in threads, which gives
 the CPU / operating system more time to allocate to the main server threads,
 as well as various other side benefits such as chat thread pooling and a
 slight reduction in latency. This commit is licensed under the Creative
 Commons Attribution-ShareAlike 3.0 Unported license.
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.
Infrequently send tab list updates.
Implement TagAPI into Spigot - much more efficient and only a dozen lines of code.