Demolishers should erase rubble

[Factoruser]

- If a demolisher destroys a building, only the "blueprint" should remain, but not the rubble image.

BTW: it would be nice if the demolishers would have a better AI. I.e. they'll stop chasing you at their territory's border resp. "fight" shortly with other demolishers (and retreat) if they come too close together.

I think the demolishers should spit something on the player or strike with electrical charges rather than summoning a "cloud nova" and lava eruptions, but I don't mind.