Add the ability to use schematics from Handle Schematics mod

[Alatarius]

Describe alternatives you've considered
I would like to see the ability to use schematics from Handle Schematics as an alternative to World Edit.

Saving and loading schems from this mod is easier and more reliable than world edit for handling schematics. Plus H-S doesn't have overlapping text in the notification area as with World edit.

Additional context
Add any other context eg. screenshots about the feature request here.

[lmaddox]

I think this is specific to the building_sign subproject. I'm also partial to Handle Schematics, and would like to see such support added. Block Exchange might also be useful. I have a lot of schematics I specifically want to use with this mod, many of which cannot be included in this codebase.

#56