Fix Air Blocks

Removes air blocks from copied when running /clone. To be more precise, it removes air blocks when minecraft is deciding what blocks to add to it's region selection to then paste somewhere else. For example, let's say I cloned a box around a dirt pillar. When minecraft decides which blocks to actually clone, this mod tells it to not clone any blocks that are air blocks, and then pastes just the dirt pillar without any other air blocks nearby.