AI unit build/buy improvement; HDI and GDP data updates; demand modifier changes

- AI will build more than 50 non-infantry units at a time, depending on
how much revenue they receive.
- Modify countries' starting HDI and GDP, which takes precedence over
their database values. (Can't install the .NET Framework that allows
database editing.)
- Demand modifiers for all gov't types set to 1.f, where they used to be
lower than that for all non-MPDs.