Density guided simulation does not output energy term when density-guided-simulation-nst > 1
When using multiple-time stepping, density guided simulation does not output energy term.
Fix check-pointing for density guided simulations
Previously, checkpointing for density-guided simulations did not take
into account that the checkpointing occurs in the middle of the md-loop.
Now, the state is stored before the force-calculations, so that
simulations are restarted correctly.