Each run starts at timestep=0.

For the sake of consistency, each run starts at timestep 0.

- N_data and N_swap are now set in resumable.pbs
- join_logs uses the above vars to correctly reconstruct the 'global
  timestep" for the log.lammps* files. The kept screen file"s timestep
  is not altered.
- inputs/0.in doesn't set timestep to 0 before saving restart any more.
- inputs/1.in sets timestep to 0 straight after loading restart and
  settings.
Merge branch 'master' of https://github.com/g-rutter/MD-scripts