Add clipboard metadata to CUI protocol

**Is your feature request related to a problem? Please describe.**

After loading a schematic, it's hard to tell where it will be going.

**Describe the solution you'd like**

When a schematic is loaded, mark the position as if the same shape had been copied from the current position. When not moving, //paste would then work exactly within that area. That way, WorldEditCUI will be able to show exactly the shape it would be placed into.

**Describe alternatives you've considered**

A special selection for pasting which would move with the player.

While this would certainly be more work than just faking a selection, this would also help while cutting/pasting without saving to a schematic.