Allow selection of ranges of inserted residues

[mittinatten]

Given a pdb file with residue 1, 2, 3, 4, 4A, 4B, 4C, 5, 6, 7 selections of residue numbers should have the following behavior:

• resi 1-7: all residues including inserted residues
• resi 4: residue 4
• resi 4A: inserted residue 4A
• resi 4-5: residues 4, 4A, 4B, 4C, 5
• resi 4B-5: residues 4B, 4C and 5
• resi 4A-4C: residue 4A, 4B and 4C

[mittinatten]

This is an important expansion of the interface, but probably requires some rewriting of the selection code. Looking for volunteers 🙂