SEQRES parsing

[csbrasnett]

First go at adding parsing of SEQRES section of PDB files to check the residues present with coordinates in the pdb vs. the SEQRES entry. The check will also do basic sequence alignment to try and advise which residues are missing, and raise a warning to say which ones are.

For the future, would be good to propagate the missing residues in some form for coordinate rebuilding.

[csbrasnett]

A solution to make everyone happy, remove the NW alignment altogether and just check the seqres directly against the pdb entries. (thanks @Tsjerk for the discussion)