Breaking Changes:

* Removed IDelegatingAttributeBlock, as it's basically useless.

Changes:

* Added FluidWorldUtil.drain(World, BlockPos, Simulation), which attempts to drain a FluidVolume from that particular position in the world.
* Fixed a bug where SimpleFixedFluidInvInsertable and SimpleFixedItemInvInsertable didn't respect their respective inventories "do not modify" rule.
* Added FluidKey.fromWorld(ViewableWorld, BlockPos) -> FluidVolume for FluidWorldUtil.drain to use.
* Added a mixin to vanilla's FluidBlock to get the Fluid object contained within. 
