Allow building new railroads

[Raeder]

In the "Hitler could have won" thread, TOCarroll asked:

Will the new model of WAW have the ability to modify the supply chain at the expense of troops or research?

I think the way to handle this, over land routes anyway, would be to simply allow powers to increase rail capacity by building new railroad units in territory they control. We can already build new factories, why not railroads? These would be "at the expense of troops or research" since you would be giving up production that could have been used for troops or research to build them.

This could complicate the map display graphics somewhat, but IMHO the existing rail line graphics are pretty cheesy and should be eliminated anyway.

Sea transport can already be easily increased by building new transports.