Defines the placement of the molecules. Atoms in all lists are
considered for placement. Subclasses define the specific algorithm
for placement, and for interpretation of the different lists.
Some subclasses will simply place all atoms as if they are in a single
list, while others will place atoms in different lists in different
ways, for example to form a lattice appropriate to a compound
(i.e., a solid-box mixture).
Reads the configuration from the file and then replicates the
configuration reps times in each direction. The new configuration is
then written out to outFilename (also as binary). The density and
original number of atoms are required as input.