Add a Demand Factor to EconManager State Building weights.

[gawquon]

The problem of matching supply to demand is that we can't predict demand. Demand is partly based on the SoL of pops which is not fully under our control.

If the national market has a severe shortage of a good not produced by peasants, we could add a demand factor to make states prioritize filling severe shortages.

[Zemurin]

We can, theoretically, sum the amount of factories we already built for a specific good, divide by production method, and make a guesstimate of the required input needs. However we cannot even guesstimate sell orders.

However even to do this we'd need to do multiple construction passes - first construct industries, and then try to fill up resources to feed those industries in a second pass?