Added Gold and Iron to the Physical Assemblies

I just added two of the most known elements - Gold and Iron. I will let
the other developer do the rest. Maybe not the rest, but most of it,
because I suck at chemistry. I have also added all the initialization to
the preInit event in the class "PeriodicCraft.java".  Please keep in
mind to add the initializations here instead now. We want it all to be
very clean.