Fixed iteration numbering

Previously, when N iterations were to be calculated, model wrote
snapshots number 0, 1, 2, ..., N, i.e. an extra one. Now the numbering is
correct: 1, 2, ..., N. Also skip is effectively larger by one for
convenience reasons. E.g. when iter_num=10, readings=2 model actually writes
iterations 1, 5, 10.

Also reflected renaming data/out_pic to data/out-pic in .gitignore.