technic_chests was depending on the technic mod, for the top-level
"technic" table and the technic.swap_node function. Resolve that by
sharing the top-level table and inlining the one use of the function.
It was also depending on technic_worldgen, for the definitions of
cast iron and wrought iron. Make the use of cast iron conditional on
technic_worldgen, falling back to default "steel". Change the use of
wrought iron to directly use default "steel", to which it is aliased
anyway.
All the chests added by technic specify their material in their
description, so the description "Chest" for the default chest looks
ambiguous. Rename it to seamlessly fit into the range of chest types.
