rename -> IntegratorGK (Gauss-Kronrod) to disambiguate from

Base/Math/IntegratorGK.cpp

Base/Math/IntegratorGK.h

Sample/Aggregate/InterferenceFunction2DLattice.cpp

Sample/Aggregate/InterferenceFunction2DParaCrystal.cpp

Sample/Aggregate/InterferenceFunction2DSuperLattice.cpp

Sample/Aggregate/InterferenceFunctionFinite2DLattice.cpp

Sample/Aggregate/InterferenceFunctionHardDisk.cpp

Sample/Correlations/FTDistributions2D.cpp

Sample/Correlations/IPeakShape.cpp

Sample/HardParticle/FormFactorCone.cpp

Sample/HardParticle/FormFactorHemiEllipsoid.cpp

Sample/HardParticle/FormFactorTruncatedSphere.cpp

Sample/HardParticle/FormFactorTruncatedSpheroid.cpp

Sample/HardParticle/Ripples.cpp