[BUG] Scatter/gather of intervals uses misleading filename (content is fine)

[FriederikeHanssen]

The module create_intervals_bed uses awk magic to split up interval files into batches of similar genome size. However, for the naming of the file the first interval is being used, which can lead to the misleading impression, that some intervals are discarded. (They are not!) Fixing this would be great, i.e. by using the first and last position in the file for naming.