Add utility class AsynchronousExecutor

This class is a general purpose task execution system, that uses stages
to separate processing blocks for asynchronous and synchronous
executions.
Add RegionFile from mc-dev for diff visibility
Load chunks asynchronously for players.

When a player triggers a chunk load via walking around or teleporting there
is no need to stop everything and get this chunk on the main thread. The
client is used to having to wait some time for this chunk and the server
doesn't immediately do anything with it except send it to the player. At
the same time chunk loading is the last major source of file IO that still
runs on the main thread.

These two facts make it possible to offload chunks loaded for this reason
to another thread. However, not all parts of chunk loading can happen off
the main thread. For this we use the new AsynchronousExecutor system to
split chunk loading in to three pieces. The first is loading data from
disk, decompressing it, and parsing it in to an NBT structure.  The second
piece is creating entities and tile entities in the chunk and adding them
to the world, this is still done on the main thread. The third piece is
informing everyone who requested a chunk load that the load is finished.
For this we register callbacks and then run them on the main thread once
the previous two stages are finished.

There are still cases where a chunk is needed immediately and these will
still trigger chunk loading entirely on the main thread. The most obvious
case is plugins using the API to request a chunk load. We also must load
the chunk immediately when something in the world tries to access it. In
these cases we ignore any possibly pending or in progress chunk loading
that is happening asynchronously as we will have the chunk loaded by the
time they are finished.

The hope is that overall this system will result in less CPU time and
pauses due to blocking file IO on the main thread thus giving more
consistent performance. Testing so far has shown that this also speeds up
chunk loading client side although some of this is likely to be because
we are sending less chunks at once for the client to process.

Thanks for @ammaraskar for help with the implementation of this feature.
Fix EntityEquipment positions being reversed. Fixes BUKKIT-3157
Add isRecord and new material method tests.

Cleaned up all of the CraftBukkit tests, including moving some tests
from MaterialTest to PerMaterialTest.
ItemStack.asBukkitStack(null) should return Air. Fixes BUKKIT-3170
Implement ItemFactory and ItemMeta values. Adds BUKKIT-15
Clarify functionality in CraftInventory. Fixes BUKKIT-3097

Changes some NPEs to IllegalArgumentExceptions for exception consistency.

Contains(ItemStack, int) correctly calculates number of ItemStacks.

Adds a containsAtLeast(ItemStack, int) for finding a combined amount of a
single similar ItemStack.

Makes some utility methods private to prevent ambiguity in use.
Change enchantment comparisons to isSimilar. Fixes BUKKIT-3183

The purpose of the isSimilar method was designed to consider all NBT
data, not solely enchantments, without the need to have exact stack
size matches. The respective methods in CraftInventory were still
comparing enchantments instead of the ItemMeta.
Refactor get/setChestPlate to Chestplate. Addresses BUKKIT-3189
Add missing name in PotionEffect for Wither
Fix PotionMeta not applying the correct Id. Fixes BUKKIT-3193
[Bleeding] Check visibility API for sounds. Fixes BUKKIT-3114

With 1.4, entity sound tracking changed for the better.
Our previous method additions can now be removed.
All that's left is checking if the source can be seen
by the recipient of the sound packet. Thanks, Mojang!
Updated version to 1.4.5-R1.0 in pom.xml for RB.
Updated version to 1.4.5-R1.1-SNAPSHOT for development towards next release.
Happy fun time with spoofing