Merge branch 'per-action-restart'

regtest/basic/rt10-restart/H1

regtest/basic/rt10-restart/bck.0.H1.reference

regtest/basic/rt10-restart/plumed.dat

regtest/basic/rt19/COLVAR.nores.gz

regtest/basic/rt19/bck.0.COLVAR.nores.gz.reference

regtest/basic/rt19/plumed.dat

src/analysis/Analysis.cpp

src/bias/MetaD.cpp

src/core/Action.cpp

src/core/Action.h

src/core/ActionSetup.cpp

src/setup/Restart.cpp

src/tools/OFile.cpp