[MRG] Remove nulled drives during convert to hierarchical json function

[gtdang]

Updated the hierarchical json conversion script to prune nulled drives. Legacy param files had placeholders for several drives. If unused, values out of typical ranges were specified to null those drives. Typically this occurs when a start time is set greater than the stop time or if weights are set it negatives or 0s. The hierarchical json format will not include drives with bad parameters.

Questions

1. Are the filters for nulled drives correct/complete?
   • Check for start < stop
   • Checks nmda and amps weights for at least one >0 value