Add 'buried residues' track to protein viewer

[ValWood]

from
#1126 (comment)

pdb have a track called "buried residues"
This will only be available for proteins with pdb structures, but it would be a nice addition to the protein feature viewer if we can get the data from pdb (it should anti-correlate with modified residues)

see https://www.rcsb.org/sequence/4ro1

[ValWood]

@kimrutherford I think you looked into this and could not see the data?
(Note that this track would only be available for proteins with structures, I think)

if you can't see where to access it we can put "blue sky" on this one.