Added support for ring-destruction-model elements.
The getProductionTypes function now handles the case where an attribute is missing, removing the need for a try-except around every call to that function.
Fixed a bug where the same ControlProtocol would accidentally get assigned to multiple production types.
Problem with test file: the ring vaccination rules say that pigs will be vaccinated, but no vaccine effect parameters were specified for pigs.
Now handles vaccination.
Fixed a syntax error and outdated field names in the SQL query.
Fix to handle NULL values in the destruction program delay and destruction capacity fields.
Cleanup: because the number of possible reasons for destruction is fixed (both in the fields that exist in the database, and in the enumeration SPREADMODEL_control_reason, there is no need for DeclarationOfDestructionReasons events.