Refactored parts relating to LandCoverType

GAMS/IntExtOpt.gms

src/ac/ed/lurg/ModelConfig.java

src/ac/ed/lurg/ModelMain.java

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

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

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

src/ac/ed/lurg/landuse/CarbonFluxItem.java

src/ac/ed/lurg/landuse/CarbonFluxReader.java

src/ac/ed/lurg/landuse/LandCoverChangeItem.java

src/ac/ed/lurg/landuse/LandCoverReader.java

src/ac/ed/lurg/landuse/LandUseItem.java

src/ac/ed/lurg/landuse/WoodYieldItem.java

src/ac/ed/lurg/landuse/WoodYieldReader.java

src/ac/ed/lurg/output/LpjgOutputer.java

src/ac/ed/lurg/types/GamsLandCoverType.java

src/ac/ed/lurg/types/LandCoverType.java