Implemented five-column score file -- only during concatenation

Closes #85 (closed)

I have implemented the fifth column only during concatenation, where I add the model_id as the second column.

New test case is implemented, so we should be ready to go.

@andre.anjos I have assigned this PR to you since I believe you know most of the score file formats. Feel free to re-assign.

mentioned in commit 24f54913

merged