Refactor: Move fuel to reactor level

No longer in control rods. Fuel is now in the reactor itself.
This is mostly untested aside from assembly and fueling.
Reactor update packets are now also handled in the reactor themselves.
Fuel rod ISBRH, removing control rod ISBRH, fixes #74

More of a sidestep than a fix. Control rods themselves aren't rendered,
but that's fine as in 99.9% of cases you couldn't see them anyway