Module loader now instantiates trace quarantine model whenever tracing is being used. Simplified that module - it was overly complicated with options for contact type, direction, and production type. That module doesn't need options because the model spec simply states "When a unit in which disease has not been previously detected is identified by a trace investigation, it will be quarantined."
Some simplifications now that spreadmodel_read_prodtype returns just a single production type. Also fixes to the SQL query now that some fields have dropped "_pdf_id" in favor of just "_id".
Minor: deleted an unneeded function.
Some simplifications now that spreadmodel_read_prodtype returns just a single production type and spreadmodel_read_zone returns just a single zone.