Obtain information for building from PDB header

[dww100]

In line with the design outline we need to get information out of a PDB file in order to use in system building.

We have decided to base the workflow on ParmEd. For information we definitely need I will start issue in the ParmEd fork issue tracker and link here. Discuss things you think need to be added below and if you add a relevant issue in ParmEd mention here please.

A full list of PDB records is available here but we probably only need a subset of this information.

Definitely need:

BIOMT UCL-CCS/ParmEd#1
SEQRES UCL-CCS/ParmEd#2
SSBOND UCL-CCS/ParmEd#3

Maybe useful:
Missing atom lists
Missing residue lists
HET information (HET, HETNAM, FORMUL)

[dww100]

Header reader code now in BAC - however only looks for BIOMT and SEQRES for now. Part of general move to use ParmEd as a library 'as is' and bring functionality into BAC.

ParmEd appears to do a good job of detecting disulphide bonds and putting in bonds list. We should make use of this.