Made it so that WHAM histogram is only output by one replica

regtest/analysis/rt-wham/fes.0.dat.reference

regtest/analysis/rt-wham/plumed.dat

regtest/analysis/rt-wham/wham-weights.0.reference

src/analysis/OutputColvarFile.cpp

src/analysis/ReadAnalysisFrames.cpp

src/analysis/ReadAnalysisFrames.h

src/bias/ReweightBase.h

src/bias/ReweightWham.cpp

src/bias/ReweightWham.h

src/gridtools/GridPrintingBase.cpp

src/gridtools/GridPrintingBase.h

src/vesselbase/ActionWithAveraging.cpp