Add creeper hostility

[Caaz]

Creepers currently are factionless, colonists aren't afraid of them. That should be fixed, and can be done via a hidden creeper faction or by utilizing mechanoids or insects. Alternatively, patching IsHostile would also work. There's probably some other decent ways too.

From Vukanshak.

[...] or they can be seen as a threat by colonists and get shot at, since colonists just ignore them until its too late!