Added feature to output loss ratios (not just absolute loss values)

https://git.gfz-potsdam.de/cnievas/real-time-loss-tools/-/merge_requests/25 added a feature to post-process individual outputs into collective outputs. Up to this point, all outputs were absolute values (e.g. loss in euros, number of people injured/dead).

The present MR generates outputs in terms of loss ratio (% of total replacement cost of buildings, % of total number of census occupants) as well.