Damaged by terrain

This is a trait that replaces the PoisonedByTiberium trait for a more general approach, this now not only works on resources but also on terrain, have a unit that cant live on anything but tiberium add Clear and Beach to the Terrain variable (you might need to add Rough too but I have no idea what terrain that is).
I'll assume that this needs to be remedied, though. (not necessarily in this PR)