Added NBT writing and reading to TileEntityDirtChest.  Now you can store things in them and they'll actually save!
Added a Slot subclass that actually checks with the tile entity whether or not an item is acceptable in it.  Updated the Tile Entity to include a check against Dirt.

However, there is still one last little problem: Non-dirt items can still be placed into the cehst if the user shift-clicks!  Must need to update ContainerDirtChest#transferStackInSlot()...