merge subsidies changes

GAMS/IntExtOpt.gms

GAMS/LUOpt.gms

data/subsidyrates.csv

src/ac/ed/lurg/InternationalMarket.java

src/ac/ed/lurg/ModelConfig.java

src/ac/ed/lurg/ModelMain.java

src/ac/ed/lurg/country/CountryAgent.java

src/ac/ed/lurg/country/SubsidyRateManager.java

src/ac/ed/lurg/country/gams/GamsCountryInput.java

src/ac/ed/lurg/country/gams/GamsLocationOptimiser.java

src/ac/ed/lurg/demand/DemandCurve.java