Ast 586 use sorted baselines in splituvw

nsetupSplitUVW is used in OnePredict to select a subset of the uvw-coordinates to compute station based uvw-coordinates. The selected baselines span all stations, but otherwise the selection is random. That is ok for regular data, since the uvw-coordinates have redundant information. For BDA data the random selection can lead to information loss, because the uvw-coordinates of long baselines is at higher resolution in time and frequency.

This MR introduces an overload of nsetupSplitUVW that accepts the station positions as extra parameter, which is used to select the set of longest baselines that span all stations.