huge .gro files handling: >99999 residues

[hernanchavezthielemann]

Describe the bug
files with more than 99999 residues have not yet been handled

Expected behavior
the idea is to add 100000 when 99999 is surpassed

Problems
the problem is that residue numbering could be sometimes messy/unordered

so the solution :

if res_id[i-1] < res_id[i]  and res_id[i] == 0:
     res_id_base = 100000
res_id[i] += res_id_base

its not an option