WebSandboxMC

• Fix slow initial world load performance by sending chunk data compressed in one binary frame, now several times faster (GH-86)
• Add logging when a new web client joins, showing their username and address (GH-84)
• Fix excessive Netty logging, now sent at debug level by default, can be re-enabled at info level with netty_log_info option if needed (GH-84)
• Tested with 1.12-pre6

Update to NetCraft build 456:

• Add support for compressed multi-block updates (b, command) for much faster loading than per-block (B, command) updates (satoshinm/NetCraft#136)