Use item entity ticking optimization from TickThreading. Fixes #1354

Skip ticks while properly updating motion to match client prediction.
Fixes the 'choppy' item drop movement.

Thanks to nallar and OniBait for the original code - TickThreading by
nallar, and MCPC+ integration by OniBait originally in:
MinecraftPortCentral/MCPC-Plus@cd208eb20f687cbde9dee9081d5270fcc89da6a9