This is the new pipe_control.structure.main.assemble_structural_coordinates() function. It takes
the sequence alignment logic out of the lib.structure.internal.coordinates.assemble_coord_array()
function so that sequence alignments in the relax data store can be used. The logic has also been
redefined as: 1, use a sequence alignment from the relax data store if present; 2, use no sequence
alignment if coordinates only come from structural models; 3, fall back to a residue number based
alignment. The residue number based alignment is yet to be implemented.
As a consequence, the lib.structure.internal.coordinates.assemble_coord_array() function has been
greatly simplified. It no longer handles sequence alignments, but instead expects the residue
skipping data structure, built from the alignment, as an argument. The seq_info_flag argument has
also been eliminated in this function as well as the pipe_control.structure.main module.
