Add getWorld() , update() and set-getUsePhysics

There are many cases in vanilla where a player can cause a block to be in a state where it will do something if it gets a block update, without causing a block update. For example, any of the block update detector designs.

The ability to trigger a block update without changing anything else may be useful in plugins which add extra redstone features such as a sponge equivalent of [craftbook](http://dev.bukkit.org/bukkit-plugins/craftbook/).