Report energy_correction in __repr__ of a Configuration.

This is essential in producing correct arkane input files, because
the configurations are just printed using str().
Without this offset, all your energies are wrong.

See #2791.
I think this might address the bug, but there might be other improvements
that can be made.
(At very least, making this less fragile!)

Author: rwest

rmgpy/pdep/configuration.pyx

@@ -73,6 +73,7 @@ cdef class Configuration(object):
         if self.sum_states is not None: string += 'sum_states={0}, '.format(self.sum_states)
         string += 'active_k_rotor={0}, '.format(self.active_k_rotor)
         string += 'active_j_rotor={0}, '.format(self.active_j_rotor)
+        if self.energy_correction != 0.0: string += 'energy_correction={0}, '.format(self.energy_correction)
         string += ')'
         return string