More changes for trigger support:
+ Change qso execute signature and replace the SSConnection param with ExecutionState.
  ExecutionState holds the SSConnection as well as any late binding constant values.  Propagate the
  signature change everywhere.
+ Add a trigger qso, whose role is to obtain the trigger rows, execute the appropriate update,
  and execute both before and after trigger bodies.
+ Change the trigger execution step to represent the row query as an ExecutionStep so that we can
  just execute the scheduled qso with a captured result consumer.
+ Add binding for late constants to SQLCommand, GenericSQLCommand.  Arrange for the binding to
  occur at the time pertinent qsos execute.
+ Change transform test infrastructure to reflect new trigger execution step.