Implement some basic multiblock validation

[MasterEnderman]

We already have the highlighter so might as well add helpers for
Hollow / filled AxAxB (square footprint, variable height) structures, maybe even differentiate where to place the controller, similar to the reactors in alchemistry or centered on the top or bottom of the structure.

[MasterEnderman]

Maybe even get super fancy with it and allow external hatches for in and outputs.
But I have no idea how to tackle that right now.