In ultramine core player data saves asynchronously, so it was possible to read OLD data after
NEW data requested to save, but has not really been written to the file.

Now we don't wait for finishing of writing all worlds. Waiting only for current world, then closing region files. Currently implemented for ImportChunkLoader only, should be implemented for default chunk loader in future

This reverts commit 3aa3ad9.
(Issues with some mods that uses random seed)

Newly populated chunk contains lots of PendingBlockUpdate and EntityFallingBlock, that takes lot of memory. PendingBlockUpdate processing causes more EntityFallingBlock spawning. In its turn, processing of EntityFallingBlock causes PendingBlockUpdate scheduling again. It solves by multiple iterations of processing both PendingBlockUpdate and EntityFallingBlock. Finally, we removing any EntityItem, that may be spawned at that time

Now we calling utilizeCPU method instead of Thread.sleep in in main server loop. In this method we can do something more useful than sleep. Currently implemented SyncServerExecutor queue processing and chunk generation

- min player moved distance is now directly proportional to viewDistance
- used back sort for toSend list (to remove values from end of list without copying)
- toSend list is now sorting only before sending (if necessary)
- removed unnecessary setWorldDestroyed method