Add functionality to calculate the integral of a grid and to use this as a cv

regtest/analysis/rt-integral/Makefile

regtest/analysis/rt-integral/colvar.reference

regtest/analysis/rt-integral/config

regtest/analysis/rt-integral/forces.reference

regtest/analysis/rt-integral/plumed.dat

regtest/analysis/rt-integral/trajectory.xyz

regtest/analysis/rt-uweights-integral/Makefile

regtest/analysis/rt-uweights-integral/colvar.reference

regtest/analysis/rt-uweights-integral/config

regtest/analysis/rt-uweights-integral/forces.reference

regtest/analysis/rt-uweights-integral/plumed.dat

regtest/analysis/rt-uweights-integral/trajectory.xyz

regtest/analysis/rt-weights-integral/Makefile

regtest/analysis/rt-weights-integral/colvar.reference

regtest/analysis/rt-weights-integral/config

regtest/analysis/rt-weights-integral/forces.reference

regtest/analysis/rt-weights-integral/plumed.dat

regtest/analysis/rt-weights-integral/trajectory.xyz

src/analysis/Analysis.h

src/analysis/Average.cpp