updates icon paths in multiple files
removed insulated icon state in pipe_item.dmi (insulateds are deaaaad)
lays an icon framework so that o2 generators, cold sinks, heat sinks may eventually be made constructable
they no longer override update_icon() but instead update like just about every other device
eventually I'll give these real sprites but given that they're unused it can wait for now
sprites and construction are outside the scope of this PR
makes heat exchangers update their color based on their node
because heat exchangers are different sprite-wise they had to override update_icon entirely
makes heat exchanger, heat sinks, cold sinks, o2 generators non-dense
dab13732fe