Building sidewalk with rubble

A remix of my original building sidewalk and the cool rubble generator. This is still a work in progress, but I'm not going to have time to work on it for a bit, so I wanted to upload it.

The idea is to put the Dropzone buildings in the slots to keep them square, and then if someone demolishes the building, you remove the building but keep the sidewalk in place revealing the rubble.

Things to do still:
* Make it so that the random numbers are given a seed so we can have predicable/recreatable rubble
* ensure that the height of the rubble is correct according to the rules.
* make sure it's customizer friendly