BayDAG Contribution #11: School Escorting Estimation Updates

[dhensle]

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Most changes in this PR are needed to avoid crash if estimation run actually had no school escorting in the input data. Empty school escorting tables are not handled appropriately in the current implementation. This would arise when running estimation mode with a small enough sample that school escorting was not included in the estimation data.

Additional fixes in this PR fix a case where the "gender weight" optional setting used to rank chauffeurs was incorrectly using the person weight setting instead. It also appropriately names the alternative column for estimation mode (see #771).

Required for SANDAG ABM3 production? -- No