Resolved a random deadlock that became way too frequent to ignore

There was a deadlock that sometimes occurred when passing PacketSetBlock
to client: PacketSetBlock first acquired monitor of the chunk it
modified, than attempted to lock the visible chunks set. In parallel, a
chunk update first acquires the visible chunks, than the individual
chunk. Turns out, markForUpdate() doesn't need to be synchronized, so
PacketSetBlock can now acquire the locks sequentially, avoiding the
deadlock.

src/main/java/ru/windcorp/progressia/client/world/ChunkRender.java

@@ -97,7 +97,7 @@ public class ChunkRender
 		return data;
 	}
 
-	public synchronized void markForUpdate() {
+	public void markForUpdate() {
 		getWorld().markChunkForUpdate(getPosition());
 	}