Dd selection

Updated split-directions. This version of split-directions is compatible with toil-cwl-runner, replaces the concatenation with 1 Python script which calls DP3 and takes care of placing necessary dummy MS for frequency gaps, and includes scalarphasediff calibrator selection metrics described in de Jong et al. (2024). This version of split-directions has been tested by several people, including Leah, Frits, Neal, and Jurjen.