Split seismic data used in GEN_OBS into one file per region

[oddvarlia]

For some localisation setup in ERT where there are isolated regions or segments, one want to only let observations relevant for the segment be used and not include correlations between observations outside the segment and model parameters located inside the segment. To achieve this for seismic observations, it should be possible to choose only the seismic observations within a segment and have one GEN_OBS keyword for seismic data per seismic attribute per segment. A script splitting the seismic observations into one file per segment is necessary in this case.