Approved residues for each segment: make this info available to scripts and mutate tool

[Bruno Kestemont]

I would be interested to be able to retrieve, with a script, the info on Approved residues that we can read from each segment pushing on Tab.

This would allow to write scripts (like Mutate combo) that would only try approved residues (saving time and filter losses).

Another related suggestion is highlighting, in the Mutate tool, the approved residues. The same kind of tool was asked for GUI some time ago:
https://fold.it/portal/node/994635