Ability to declare nodes as radiation protection and corium-resistant

[alerikaisattera]

The list of radiation shielding nodes is hardcoded and cannot be changed by external mods. I suggest either adding a group or API method for registering custom radiation protection nodes

For corium, I suggest adding a group that makes nodes in that group unaffected by corium

[DustyDave961]

I have created a fork with a possible fix, but I have not been able to properly playtest it.