Use the residue numbers from the original PDB structure

[lafita]

We are currently using the sequential index of the residue in the structure but this might generate problems with structures with missing residues (although method should not work on those) and makes the mapping and visualization harder.

Try to use/display the residue numbers from the PDB file.

[lafita]

A better solution would be to provide both the sequential and PDB residue indices so that user can use both. For missing residues in the middle of the structure this is related to issue #6