fetchNASIS: add summaries of phorizon child tables for bulk density and Ksat

[brownag]

Currently there is no way to get the following pedon horizon child tables in soilDB without a custom query and aggregation

• phdb Pedon Horizon Bulk Density
• phksatsummary Pedon Horizon Ksat Summary

Aggregation considerations:

• phdb
  • multiple observations per genetic horizon, top and bottom depth required
  • multiple methods (probably don't want to aggregate dissimilar methods)
  • field moist/air dry source data/subsamples vs. calculated outputs
• phksatsummary
  • possible multiple test dates
  • multiple methods (amoozemeter, double/single ring, saturo [to be added])
• General
  • Some source data / values needed for calculations are stored in child tables

Other issues:

• Planned updates to data model for DSP may break anything we develop for current model (not sure on timeline for updates)