Expanding & Overviewing the map

[xoft]

Plan of action:
- Implement a cWorld::PrepareChunk() method that either loads the chunk from disk or generates it, as needed, and lights it.
- (Use that function in cSpawnPrepare for cWorld - https://github.com/mc-server/MCServer/issues/1615 )
- Export the function to Lua
- Change the ChunkWorx plugin to use the function instead of cWorld:TouchChunk()
- Change the ChunkWorx plugin to use a better queueing and smarter chunk ordering.