Bug fix release

Bug fixes:

- When Configuration objects were copied, the cell parameters were not copied.
  The copy contained the cell parameters of the current configuration of the
  universe instead.

- Nonbonded list generation for periodic universes could in rare cases
  miss atom pairs inside the cutoff.

- Multi-threaded energy evaluation got stuck for more than two threads.

- Dihedral energy terms were wrong for phase offsets other than
  0 and pi. Note: this has no incidence on AMBER and OPLS force fields
  because they use only offsets of 0 and pi.

- The charges for the Amber force field in the database files for nucleotides
  were lacking the last digit.