Computes country-level emissions based on global carbon price

[jrising]

This provides an alternative logic path for the main model (the climate-only model is left the same). Previously (and under the climate model), the Scenario informs CO2Emissions directly. Under this new path, the Scenario feeds into the CarbonPriceInfer, which goes to AbatementCostsCO2, and from that to CO2Emissions. This allows for country-level CO2 emissions.

This also updates the country-level empirical reductions equations so that the equation [empirical reduction] / (exp(-Price / 500) + [empirical reduction]) only applies to reductions less than 100% (because we still want to allow some countries to have negative emissions).

It also fixes the use of the empirical autoregressive term, and makes the carbon price inference exactly consistent with the emissions reduction calculations in AbatementCostsCO2.