heatsinkable luac

[The4codeblocks]

prereq? for mt-mods/digistuff#88

[SmallJoker]

If digistuff depends on mesecons_luacontroller, then mesecons_luacontroller should provide some documented anchor such that mods can use core.override_item on all relevant nodes to extend its features.
It is surely possible to add this group as you proposed, but wouldn't it be easier if mods could easily do whatever they want without having to implement features directly in mesecons?